slot_nb_nonzero():  Another leak uncovered by the sandbox datetime tests.  I found the logic too confusing to follow here, so rewrote more than was likely absolutely necessary.
slot_nb_nonzero():  Another leak uncovered by the sandbox datetime
tests.  I found the logic too confusing to follow here, so rewrote more
than was likely absolutely necessary.

Bugfix candidate.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator