bpo-31626: Fix _PyObject_DebugReallocApi() (#4310)

_PyObject_DebugReallocApi() now calls Py_FatalError() if realloc()
fails to shrink a memory block.

Call Py_FatalError() because _PyObject_DebugReallocApi() erased freed
bytes *before* realloc(), expecting that realloc() *cannot* fail to
shrink a memory block.
2 files changed