Fix a compiler warning in _randommodule.c

The test just before the cast ensures that the cast cannot overflow.

Fix the warning on 32-bit Windows:

    Modules\_randommodule.c(525,28): warning C4244: '=': conversion
    from 'uint64_t' to 'Py_ssize_t', possible loss of data

Author: vstinner

Modules/_randommodule.c

@@ -522,7 +522,7 @@ _random_Random_getrandbits_impl(RandomObject *self, uint64_t k)
         PyErr_NoMemory();
         return NULL;
     }
-    words = (k - 1u) / 32u + 1u;
+    words = (Py_ssize_t)((k - 1u) / 32u + 1u);
     wordarray = (uint32_t *)PyMem_Malloc(words * 4);
     if (wordarray == NULL) {
         PyErr_NoMemory();