In some conditions the standard streams will be None or closed in the child process (for example if using "pythonw" instead of "python" on Windows). Avoid failing with a non-0 exit code in those conditions.
Report and initial patch by poxthegreat..
(cherry picked from commit e756f66c83)
* bpo-28326: Fix multiprocessing.Process when stdout and/or stderr is closed or None. (#4073)
(cherry picked from commit daeefd2e04)
* [3.6] bpo-28326: Fix multiprocessing.Process when stdout and/or stderr is closed or None. (GH-4073).
(cherry picked from commit daeefd2e04)