Always assume someoneWasListening when we get invalid notification in emityNotification()

When we get invalid entry from EntityCache in emitNotification(), we don't
emit the notification (because we don't have any item to emit it on) and
instead just skip it silently. This change makes sure that we set
someoneWasListening to true (even though we don't know if someone was really
listening), so that we avoid calling cleanOldNotifications() later, because
it's rather expensive.