add back assertion

Author: kumaraditya303

Include/internal/pycore_freelist.h

@@ -17,6 +17,11 @@ extern "C" {
 static inline struct _Py_freelists *
 _Py_freelists_GET(void)
 {
+#ifdef Py_DEBUG
+    PyThreadState *tstate = _PyThreadState_GET();
+    _Py_EnsureTstateNotNULL(tstate);
+#endif
+
 #ifdef Py_GIL_DISABLED
     PyThreadState *tstate = _PyThreadState_GET();
     return &((_PyThreadStateImpl*)tstate)->freelists;