osutil: fix excessive decref on tuple creation failure in listdir()
The stat object would be freed on error for the same reason as the previous
patch. makestat() can be inlined, but this patch doesn't change it.
https://github.com/python/cpython/blob/2.7/Python/modsupport.c#L292
The __APPLE__ code is untested.
#require docutils gettext
$ $TESTDIR/check-gendoc fr
checking for parse errors