[BUG] read_orc_statistics incorrectly reads missing statistics values as 0

[ayushdg]

Describe the bug
While reading orc_statistics with cuDF, missing attributes within a column statistics (like sum) are incorrectly read as 0.

Steps/Code to reproduce bug

import cudf
import pyorc
from io import BytesIO
import numpy as np

maxint = np.iinfo(np.int64).max

with open("numeric_overflow.orc","wb") as f:
    with pyorc.Writer(f, "struct<a:int,b:int>") as orc_writer:
        orc_writer.write((maxint, 1))
        orc_writer.write((1,1))


file_stats, stripe_stats = cudf.io.orc.read_orc_statistics(["numeric_overflow.orc"])

print(file_stats)
print(stripe_stats)

[{'col0': {'number_of_values': 2, 'has_null': False},
  'a': {'number_of_values': 2,
   'has_null': False,
   'minimum': 1,
   'maximum': 9223372036854775807,
   'sum': 0},
  'b': {'number_of_values': 2,
   'has_null': False,
   'minimum': 1,
   'maximum': 1,
   'sum': 2}}]


[{'col0': {'number_of_values': 2, 'has_null': False},
  'a': {'number_of_values': 2,
   'has_null': False,
   'minimum': 1,
   'maximum': 9223372036854775807,
   'sum': 0},
  'b': {'number_of_values': 2,
   'has_null': False,
   'minimum': 1,
   'maximum': 1,
   'sum': 2}}]

Expected behavior
The statistics values should be read is an None

 'a': {'number_of_values': 2,
   'has_null': False,
   'minimum': 1,
   'maximum': 9223372036854775807,
   'sum': None},

Environment overview (please complete the following information)

• Environment location: bare-metal
• Method of cuDF install: conda nightly (21.10)

Environment details
Please run and paste the output of the cudf/print_env.sh script here, to gather any other relevant environment details

Additional context
Seems to be a problem related to ProtoBuf default values if not checked.