Handle exceptions in get_hosts_for_room when sending events over federation

synapse/federation/transaction_queue.py

@@ -184,6 +184,7 @@ class TransactionQueue(object):
                     if not is_mine and send_on_behalf_of is None:
                         continue
 
+                    try:
                         # Get the state from before the event.
                         # We need to make sure that this is the state from before
                         # the event and not from after it.
@@ -195,6 +196,10 @@ class TransactionQueue(object):
                                 prev_id for prev_id, _ in event.prev_events
                             ],
                         )
+                    except Exception:
+                        logger.exception("Failed to calculate hosts in room")
+                        continue
+
                     destinations = set(destinations)
 
                     if send_on_behalf_of is not None: