[issue18408] Fixes crashes found by pyfailmalloc

[STINNER Victor]

STINNER Victor added the comment:

Another buildbot failure:


[150/375/4] test_ctypes
Assertion failed: __EX, file  Python/ceval.c, line 4064
Fatal Python error: Aborted

Current thread 0x00000001:
  File "/home/shager/cpython-buildarea/3.x.edelsohn-aix-ppc64/build/Lib/ctypes/test/test_random_things.py", line 44 in capture_stderr
  File "/home/shager/cpython-buildarea/3.x.edelsohn-aix-ppc64/build/Lib/ctypes/test/test_random_things.py", line 63 in test_FloatDivisionError

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue18408>
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