Update check_style.py

[dmitrishastin]

Fixes the encoding error (on Windows). Complimentary to #1935

Type

• Bug fix (non-breaking change which fixes an issue): Fixes building docs UnicodeDecodeError #1933
• New feature (non-breaking change which adds functionality). Resolves #
• Breaking change (fix or feature that would cause existing functionality to not work as expected) Resolves #

Motivation and Context

Upon running python .\util\check_style.py --apply on Windows get error:

Applying C++/CUDA style (8 processes)
multiprocessing.pool.RemoteTraceback:
"""
Traceback (most recent call last):
  File "C:\anaconda3\lib\multiprocessing\pool.py", line 125, in worker
    result = (True, func(*args, **kwds))
  File "C:\anaconda3\lib\multiprocessing\pool.py", line 48, in mapstar
    return list(map(*args))
  File "C:\Open3d\util\check_style.py", line 82, in _check_style
    is_valid_header = f.read().startswith(CppFormatter.standard_header)
  File "C:\anaconda3\lib\encodings\cp1252.py", line 23, in decode
    return codecs.charmap_decode(input,self.errors,decoding_table)[0]
UnicodeDecodeError: 'charmap' codec can't decode byte 0x90 in position 9393: character maps to <undefined>

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "C:\Open3d\util\check_style.py", line 447, in <module>
    main()
  File "C:\Open3d\util\check_style.py", line 409, in main
    changed_files_cpp, wrong_header_files_cpp = cpp_formatter.run(
  File "C:\Open3d\util\check_style.py", line 118, in run
    is_valid_files = pool.map(
  File "C:\anaconda3\lib\multiprocessing\pool.py", line 364, in map
    return self._map_async(func, iterable, mapstar, chunksize).get()
  File "C:\anaconda3\lib\multiprocessing\pool.py", line 771, in get
    raise self._value
UnicodeDecodeError: 'charmap' codec can't decode byte 0x90 in position 9393: character maps to <undefined>

Which is fixed by adding encoding='utf-8' to open() in check_style as per stackoverflow

Checklist:

• I have run python util/check_style.py --apply to apply Open3D code style
  to my code.
• This PR changes Open3D behavior or adds new functionality.
  • Both C++ (Doxygen) and Python (Sphinx / Google style) documentation is
    updated accordingly.
  • I have added or updated C++ and / or Python unit tests OR included test
    results (e.g. screenshots or numbers) here.
• I will follow up and update the code if CI fails.
• For fork PRs, I have selected Allow edits from maintainers.

Description

---

This change is 

[update-docs]

Thanks for submitting this pull request! The maintainers of this repository would appreciate if you could update the CHANGELOG.md based on your changes.

[benjaminum]

Reviewable status: 0 of 1 files reviewed, all discussions resolved