[3.12] gh-115136: Fix possible NULL deref in getpath_joinpath() (GH-115137) (GH-115157)

(cherry picked from commit 9e90313)

Signed-off-by: Artem Chernyshev <artem.chernyshev@red-soft.ru>
Co-authored-by: Artem Chernyshev <62871052+dTenebrae@users.noreply.github.com>

Author: miss-islington

Modules/getpath.c

@@ -259,6 +259,10 @@ getpath_joinpath(PyObject *Py_UNUSED(self), PyObject *args)
     }
     /* Convert all parts to wchar and accumulate max final length */
     wchar_t **parts = (wchar_t **)PyMem_Malloc(n * sizeof(wchar_t *));
+    if (parts == NULL) {
+        PyErr_NoMemory();
+        return NULL;
+    }
     memset(parts, 0, n * sizeof(wchar_t *));
     Py_ssize_t cchFinal = 0;
     Py_ssize_t first = 0;