Only loop timeout task if there's more work

Previously this would repeat the task even the current iteration of
the loop had processed a non-full batch. This could cause the task
to error incorrectly if one or two notifications breach the timeout
threshold in between iterations.

app/celery/nightly_tasks.py

@@ -155,7 +155,7 @@ def timeout_notifications():
                           len(technical_failure_notifications), [str(x.id) for x in technical_failure_notifications])
             raise NotificationTechnicalFailureException(message)
 
-        if len(notifications) == 0:
+        if len(notifications) < 100000:
             return
 
     raise RuntimeError("Some notifications may still be in sending.")