Fix rare notifier bug where listeners dont timeout

There was a race condition that caused the notifier to 'miss' the
timeout notification, since there were no other checks for the timeout
this caused listeners to get stuck in a loop until something happened.

synapse/handlers/sync.py

@@ -510,6 +510,7 @@ class SyncHandler(object):
         Returns:
             Deferred(SyncResult)
         """
+        logger.info("Calculating sync response for %r", sync_config.user)
 
         # NB: The now_token gets changed by some of the generate_sync_* methods,
         # this is due to some of the underlying streams not supporting the ability