Delete pubsub closure to `_pubsub_close()`.

The Redis channel may be closed, and in that case we need to handle the
exception instead of throwing it - which causes the upstream Tornado
worker to fail too.

platypush/backend/http/app/mixins/__init__.py

@@ -65,8 +65,7 @@ class PubSubMixin:
         with self._pubsub_lock:
             # Close and free the pub/sub object if it has no active subscriptions.
             if self._pubsub is not None and len(self._subscriptions) == 0:
-                self._pubsub.close()
-                self._pubsub = None
+                self._pubsub_close()
 
     @staticmethod
     def _serialize(data: MessageType) -> bytes: