readObjectHeader: Allow extra whitespace before "obj"

The header being read has the format:

    <idnum> <generation> obj

where `<idnum>` and `<generation>` are integers.
Previously an arbitrary number of spaces was being allowed between `<idnum>` and `<generation>`, but not between `<generation>` and `obj`.
We now allow arbitrary spaces between `<generation>` and `obj`.

PyPDF2/pdf.py

@@ -39,11 +39,19 @@
 __maintainer__ = "Phaseit, Inc."
 __maintainer_email = "[email protected]"
 
+import codecs
 import math
 import struct
 import sys
 import uuid
+import warnings
 from sys import version_info
+
+from . import utils
+from .generic import *
+from .utils import (ConvertFunctionsToVirtualList, b_, formatWarning, isString,
+                    ord_, readNonWhitespace, readUntilWhitespace, str_, u_)
+
 if version_info < ( 3, 0 ):
     from cStringIO import StringIO
 else:
@@ -54,12 +62,6 @@
 else:
     from io import BytesIO
 
-from . import utils
-import warnings
-import codecs
-from .generic import *
-from .utils import readNonWhitespace, readUntilWhitespace, ConvertFunctionsToVirtualList
-from .utils import isString, b_, u_, ord_, str_, formatWarning
 
 if version_info < ( 2, 4 ):
    from sets import ImmutableSet as frozenset
@@ -1734,6 +1736,7 @@ def readObjectHeader(self, stream):
         idnum = readUntilWhitespace(stream)
         extra |= utils.skipOverWhitespace(stream); stream.seek(-1, 1)
         generation = readUntilWhitespace(stream)
+        extra |= utils.skipOverWhitespace(stream); stream.seek(-1, 1)
 
         # although it's not used, it might still be necessary to read
         _obj = stream.read(3)  # noqa: F841