[issue31718] some methods of uninitialized io.IncrementalNewlineDecoder objects raise SystemError

[Serhiy Storchaka]

Change by Serhiy Storchaka <storchaka+cpython at gmail.com>:


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nosy: +benjamin.peterson, stutzbach
versions: +Python 2.7, Python 3.6

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue31718>
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