closes bpo-34501: PyType_FromSpecWithBases: Check spec->name before dereferencing it. (GH-8930)

Reported by Svace static analyzer.

Author: Alexey Izbyshev

Objects/typeobject.c

@@ -2847,15 +2847,22 @@ PyType_FromSpecWithBases(PyType_Spec *spec, PyObject *bases)
     char *res_start = (char*)res;
     PyType_Slot *slot;
 
+    if (res == NULL)
+        return NULL;
+
+    if (spec->name == NULL) {
+        PyErr_SetString(PyExc_SystemError,
+                        "Type spec does not define the name field.");
+        goto fail;
+    }
+
     /* Set the type name and qualname */
     s = strrchr(spec->name, '.');
     if (s == NULL)
         s = (char*)spec->name;
     else
         s++;
 
-    if (res == NULL)
-        return NULL;
     type = &res->ht_type;
     /* The flags must be initialized early, before the GC traverses us */
     type->tp_flags = spec->flags | Py_TPFLAGS_HEAPTYPE;
@@ -2865,8 +2872,6 @@ PyType_FromSpecWithBases(PyType_Spec *spec, PyObject *bases)
     res->ht_qualname = res->ht_name;
     Py_INCREF(res->ht_qualname);
     type->tp_name = spec->name;
-    if (!type->tp_name)
-        goto fail;
 
     /* Adjust for empty tuple bases */
     if (!bases) {