[docs] Clarify max_length and flush() for zlib decompression (issue 23200)

Reviewers: , https://bugs.python.org/review/23200/diff/15974/Lib/zipfile.py File Lib/zipfile.py (right): https://bugs.python.org/review/23200/diff/15974/Lib/zipfile.py#newcode922 Lib/zipfile.py:922: not data and Actually I think this condition also needs to fail if any compressed data was passed in: compressed_data = data # Before decompression if ... not compressed_data and not data and ... Please review this at https://bugs.python.org/review/23200/ Affected files: Doc/library/zlib.rst Doc/whatsnew/3.6.rst Lib/encodings/zlib_codec.py Lib/test/test_codecs.py Lib/test/test_zlib.py Lib/zipfile.py Misc/NEWS Modules/zlibmodule.c