bpo-37732: Fix GCC warning in _PyObject_Malloc() (GH-15333) (GH-15342)

pymalloc_alloc() now returns directly the pointer, return NULL on
memory allocation error.

allocate_from_new_pool() already uses NULL as marker for "allocation
failed".

(cherry picked from commit 18f8dcfa10d8a858b152d12a9ad8fa83b7e967f0)
1 file changed