Potential issue with early return in subscribers hook implementation

[jhedstrom]

If this code in message_subscribe_message_subscribe_get_subscribers is ever triggered:

      if ($range) {
        --$range;
        if ($range == 0) {
          // We've reach the requested item.
          return $uids;
        }

it may cause issues when complex contexts are used, since in that event each entity type is looped through. If a user with a lower uid is subscribed to an entity that hasn't been processed when this exits early, that user would not be processed in subsequent queue runs.