Reproduce, fix unexpected exception when processing zero byte file

[vinceatbluelabs]

Replace it with an expected exception with a better error message that comes from Pandas.

Before:

(records-mover-3.8.2) ]0;graybookprobroz@graybookpro:~/src/records-mover$ mvrec file2url ./empty.csv s3://bluelabs-scratch/vince.broz/bar.csv

10:09:33 - Starting...
10:09:34 - Mover: copying from DataUrlRecordsSource(None) to DataUrlTarget by first writing DataUrlRecordsSource(None) to DelimitedRecordsFormat(bluelabs - {'compression': None}) records format (if easy to rewrite)...
10:09:34 - Determining records format with initial_hints={'compression': None}
10:09:34 - Got unrecognized encoding from chardet sniffing: {'encoding': None, 'confidence': 0.0, 'language': None}
10:09:34 - Python could not determine newline format of file.
10:09:34 - 
Traceback (most recent call last):
  File "/Users/broz/src/records-mover/records_mover/records/job/mover.py", line 37, in run_records_mover_job
    return records.move(source, target, processing_instructions)
  File "/Users/broz/src/records-mover/records_mover/records/mover.py", line 93, in move
    with records_source.\
  File "/Users/broz/.pyenv/versions/3.8.2/Python.framework/Versions/3.8/lib/python3.8/contextlib.py", line 113, in __enter__
    return next(self.gen)
  File "/Users/broz/src/records-mover/records_mover/records/sources/data_url.py", line 46, in to_fileobjs_source
    with FileobjsSource.\
  File "/Users/broz/.pyenv/versions/3.8.2/Python.framework/Versions/3.8/lib/python3.8/contextlib.py", line 113, in __enter__
    return next(self.gen)
  File "/Users/broz/src/records-mover/records_mover/records/sources/fileobjs.py", line 55, in infer_if_needed
    sniff_hints_from_fileobjs(list(target_names_to_input_fileobjs.values()),
  File "/Users/broz/src/records-mover/records_mover/records/delimited/sniff.py", line 202, in sniff_hints_from_fileobjs
    hints = sniff_hints(fileobj, initial_hints=initial_hints)
  File "/Users/broz/src/records-mover/records_mover/records/delimited/sniff.py", line 265, in sniff_hints
    streaming_hints.update(python_inferred_hints)  # type: ignore
UnboundLocalError: local variable 'python_inferred_hints' referenced before assignment
(records-mover-3.8.2) ]0;graybookprobroz@graybookpro:~/src/records-mover$ 

After:

(records-mover-3.8.2) �]0;graybookpro�broz@graybookpro:~/src/records-mover$ mvrec file2url ./empty.csv s3://bluelabs-scratch/vince.broz/bar.csv
10:22:25 - Starting...
10:22:25 - Mover: copying from DataUrlRecordsSource(None) to DataUrlTarget by first writing DataUrlRecordsSource(None) to DelimitedRecordsFormat(bluelabs - {'compression': None}) records format (if easy to rewrite)...
10:22:25 - Determining records format with initial_hints={'compression': None}
10:22:25 - Got unrecognized encoding from chardet sniffing: {'encoding': None, 'confidence': 0.0, 'language': None}
10:22:25 - Python could not determine newline format of file.
10:22:26 - Attempting to parse with quoting: minimal
10:22:26 - Attempting to parse with quoting: None
10:22:26 - 
Traceback (most recent call last):
  File "/Users/broz/.pyenv/versions/3.8.2/envs/records-mover-3.8.2/lib/python3.8/site-packages/pandas/io/parsers.py", line 2558, in _infer_columns
    line = self._buffered_line()
  File "/Users/broz/.pyenv/versions/3.8.2/envs/records-mover-3.8.2/lib/python3.8/site-packages/pandas/io/parsers.py", line 2734, in _buffered_line
    return self._next_line()
  File "/Users/broz/.pyenv/versions/3.8.2/envs/records-mover-3.8.2/lib/python3.8/site-packages/pandas/io/parsers.py", line 2831, in _next_line
    orig_line = self._next_iter_line(row_num=self.pos + 1)
  File "/Users/broz/.pyenv/versions/3.8.2/envs/records-mover-3.8.2/lib/python3.8/site-packages/pandas/io/parsers.py", line 2891, in _next_iter_line
    return next(self.data)
StopIteration

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/broz/src/records-mover/records_mover/records/delimited/sniff.py", line 171, in csv_hints_from_pandas
    return attempt_parse(quoting='minimal')
  File "/Users/broz/src/records-mover/records_mover/records/delimited/sniff.py", line 158, in attempt_parse
    with stream_csv(fresh_fileobj, current_hints):
  File "/Users/broz/.pyenv/versions/3.8.2/Python.framework/Versions/3.8/lib/python3.8/contextlib.py", line 113, in __enter__
    return next(self.gen)
  File "/Users/broz/src/records-mover/records_mover/records/delimited/csv_streamer.py", line 69, in stream_csv
    out = read_csv(text_fileobj, **kwargs)
  File "/Users/broz/.pyenv/versions/3.8.2/envs/records-mover-3.8.2/lib/python3.8/site-packages/pandas/io/parsers.py", line 676, in parser_f
    return _read(filepath_or_buffer, kwds)
  File "/Users/broz/.pyenv/versions/3.8.2/envs/records-mover-3.8.2/lib/python3.8/site-packages/pandas/io/parsers.py", line 448, in _read
    parser = TextFileReader(fp_or_buf, **kwds)
  File "/Users/broz/.pyenv/versions/3.8.2/envs/records-mover-3.8.2/lib/python3.8/site-packages/pandas/io/parsers.py", line 880, in __init__
    self._make_engine(self.engine)
  File "/Users/broz/.pyenv/versions/3.8.2/envs/records-mover-3.8.2/lib/python3.8/site-packages/pandas/io/parsers.py", line 1126, in _make_engine
    self._engine = klass(self.f, **self.options)
  File "/Users/broz/.pyenv/versions/3.8.2/envs/records-mover-3.8.2/lib/python3.8/site-packages/pandas/io/parsers.py", line 2286, in __init__
    ) = self._infer_columns()
  File "/Users/broz/.pyenv/versions/3.8.2/envs/records-mover-3.8.2/lib/python3.8/site-packages/pandas/io/parsers.py", line 2580, in _infer_columns
    raise EmptyDataError("No columns to parse from file")
pandas.errors.EmptyDataError: No columns to parse from file

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/broz/.pyenv/versions/3.8.2/envs/records-mover-3.8.2/lib/python3.8/site-packages/pandas/io/parsers.py", line 2558, in _infer_columns
    line = self._buffered_line()
  File "/Users/broz/.pyenv/versions/3.8.2/envs/records-mover-3.8.2/lib/python3.8/site-packages/pandas/io/parsers.py", line 2734, in _buffered_line
    return self._next_line()
  File "/Users/broz/.pyenv/versions/3.8.2/envs/records-mover-3.8.2/lib/python3.8/site-packages/pandas/io/parsers.py", line 2831, in _next_line
    orig_line = self._next_iter_line(row_num=self.pos + 1)
  File "/Users/broz/.pyenv/versions/3.8.2/envs/records-mover-3.8.2/lib/python3.8/site-packages/pandas/io/parsers.py", line 2891, in _next_iter_line
    return next(self.data)
StopIteration

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/broz/src/records-mover/records_mover/records/job/mover.py", line 37, in run_records_mover_job
    return records.move(source, target, processing_instructions)
  File "/Users/broz/src/records-mover/records_mover/records/mover.py", line 93, in move
    with records_source.\
  File "/Users/broz/.pyenv/versions/3.8.2/Python.framework/Versions/3.8/lib/python3.8/contextlib.py", line 113, in __enter__
    return next(self.gen)
  File "/Users/broz/src/records-mover/records_mover/records/sources/data_url.py", line 46, in to_fileobjs_source
    with FileobjsSource.\
  File "/Users/broz/.pyenv/versions/3.8.2/Python.framework/Versions/3.8/lib/python3.8/contextlib.py", line 113, in __enter__
    return next(self.gen)
  File "/Users/broz/src/records-mover/records_mover/records/sources/fileobjs.py", line 55, in infer_if_needed
    sniff_hints_from_fileobjs(list(target_names_to_input_fileobjs.values()),
  File "/Users/broz/src/records-mover/records_mover/records/delimited/sniff.py", line 202, in sniff_hints_from_fileobjs
    hints = sniff_hints(fileobj, initial_hints=initial_hints)
  File "/Users/broz/src/records-mover/records_mover/records/delimited/sniff.py", line 268, in sniff_hints
    pandas_inferred_hints = csv_hints_from_pandas(fileobj, streaming_hints)
  File "/Users/broz/src/records-mover/records_mover/records/delimited/sniff.py", line 173, in csv_hints_from_pandas
    return attempt_parse(quoting=None)
  File "/Users/broz/src/records-mover/records_mover/records/delimited/sniff.py", line 158, in attempt_parse
    with stream_csv(fresh_fileobj, current_hints):
  File "/Users/broz/.pyenv/versions/3.8.2/Python.framework/Versions/3.8/lib/python3.8/contextlib.py", line 113, in __enter__
    return next(self.gen)
  File "/Users/broz/src/records-mover/records_mover/records/delimited/csv_streamer.py", line 69, in stream_csv
    out = read_csv(text_fileobj, **kwargs)
  File "/Users/broz/.pyenv/versions/3.8.2/envs/records-mover-3.8.2/lib/python3.8/site-packages/pandas/io/parsers.py", line 676, in parser_f
    return _read(filepath_or_buffer, kwds)
  File "/Users/broz/.pyenv/versions/3.8.2/envs/records-mover-3.8.2/lib/python3.8/site-packages/pandas/io/parsers.py", line 448, in _read
    parser = TextFileReader(fp_or_buf, **kwds)
  File "/Users/broz/.pyenv/versions/3.8.2/envs/records-mover-3.8.2/lib/python3.8/site-packages/pandas/io/parsers.py", line 880, in __init__
    self._make_engine(self.engine)
  File "/Users/broz/.pyenv/versions/3.8.2/envs/records-mover-3.8.2/lib/python3.8/site-packages/pandas/io/parsers.py", line 1126, in _make_engine
    self._engine = klass(self.f, **self.options)
  File "/Users/broz/.pyenv/versions/3.8.2/envs/records-mover-3.8.2/lib/python3.8/site-packages/pandas/io/parsers.py", line 2286, in __init__
    ) = self._infer_columns()
  File "/Users/broz/.pyenv/versions/3.8.2/envs/records-mover-3.8.2/lib/python3.8/site-packages/pandas/io/parsers.py", line 2580, in _infer_columns
    raise EmptyDataError("No columns to parse from file")
pandas.errors.EmptyDataError: No columns to parse from file
(records-mover-3.8.2) �]0;graybookpro�broz@graybookpro:~/src/records-mover$ 

[cwegrzyn]