Send an EntityUpdateEvent only if an entity has already been persisted

If an event comes from an entity that hasn't been persisted yet on the
internal storage then we wait for the entity record to be committed
before firing an event. It's better to wait a couple of seconds for the
database to synchronize rather than dealing with entity events with
incomplete objects.

platypush/entities/_engine.py

@@ -113,7 +113,7 @@ class EntitiesEngine(Thread):
         self.logger.info('Entities cache initialized')
 
     def _process_event(self, entity: Entity):
-        if self._entity_has_changes(entity):
+        if self._entity_has_changes(entity) and entity.id:
             get_bus().post(EntityUpdateEvent(entity=entity))
 
     def post(self, *entities: Entity):