plugins.topic_checking: Return False if superclass refuses.

If `BaseTopicPlugin` returns `False`, we should propagate that failed
response in `TopicAccessControlListPlugin`.

amqtt/plugins/topic_checking.py

@@ -94,3 +94,5 @@ class TopicAccessControlListPlugin(BaseTopicPlugin):
                     return False
             else:
                 return False
+        else:
+            return False