[3.12] gh-131181: Add some non-NULL assertion checks in Modules/_ctypes/_ctypes.c

[dyupina]

In the PyCData_NewGetBuffer() (file Modules/_ctypes/_ctypes.c), the PyObject_stgdict() is called, which may return NULL.
Its result is assigned to dict, then dict is dereferenced (view->format = dict->format ? dict->format : "B";).
If dict is NULL, a null pointer dereference will occur, so a check for NULL need to be added.

Similarly, in the PyCData_reduce() (file Modules/_ctypes/_ctypes.c) PyObject_stgdict(myself) may return NULL, so need to check result to prevent null pointer dereferencing.

Commit dcaf33a (Author: @encukou) fixes this problems, but it is very large and probably difficult to backport, so I suggest adding assert(); before the dereference.

This needs to be added to branches 3.1 - 3.12.
Found by Linux Verification Center (linuxtesting.org) with SVACE.

• Issue: Add some non-NULL assertion checks in Modules/_ctypes/_ctypes.c #131181

[ghost]

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[picnixz]

This needs to be added to branches 3.1 - 3.12.

Only 3.12 will get an update as other branches only accept security fixes (and 3.8 and older are EOL so they are not updated) (and since it only occurs on 3.12 and not on 3.13+)