fix UBSan failures for MultibyteStreamWriterObject

Author: picnixz

Modules/cjkcodecs/multibytecodec.c

@@ -1932,18 +1932,19 @@ mbstreamwriter_init(PyObject *self, PyObject *args, PyObject *kwds)
 }
 
 static int
-mbstreamwriter_traverse(MultibyteStreamWriterObject *self,
-                        visitproc visit, void *arg)
+mbstreamwriter_traverse(PyObject *op, visitproc visit, void *arg)
 {
+    MultibyteStreamWriterObject *self = _MultibyteStreamWriterObject_CAST(op);
     if (ERROR_ISCUSTOM(self->errors))
         Py_VISIT(self->errors);
     Py_VISIT(self->stream);
     return 0;
 }
 
 static void
-mbstreamwriter_dealloc(MultibyteStreamWriterObject *self)
+mbstreamwriter_dealloc(PyObject *op)
 {
+    MultibyteStreamWriterObject *self = _MultibyteStreamWriterObject_CAST(op);
     PyTypeObject *tp = Py_TYPE(self);
     PyObject_GC_UnTrack(self);
     ERROR_DECREF(self->errors);