message: Don't calculate deep change information for ResutlsNotifiers without callbacks
  When the notifier is just being used for async query execution there's no point
  in calculating the change information as it won't be used for anything.
diff: @@ -117,7 +117,7 @@ bool ResultsNotifier::need_to_run()
  void ResultsNotifier::calculate_changes()
  {
  size_t table_ndx = m_query->get_table()->get_index_in_group();
  - if (has_run()) {
  + if (has_run() && have_callbacks()) {
  CollectionChangeBuilder* changes = nullptr;
  if (table_ndx == npos)
  changes = &m_changes;
  