Fix missing entries in region-list #8701

RegionFactory::CheckNewRegion signal is emitted directly
after region-creation from RegionFactory::create().
At this point in time the region is not on any playlist.

This if fine for EditorSources, but the new RegionList design
only shows regions that are on the timeline.

CheckNewRegion() -> EditorRegions::add_region()
-> EditorRegions::regions_changed() ignores regions w/o playlist.

Later Playlist::add_region_internal() sets the playlist but
calls Region::clear_changes() to not send all individual changes.
So Region::RegionsPropertyChanged is not emitted either.

We need to notify the EditorRegions *after* setting the playlist.
The downside of this is that more signals than necessary are
emitted.

libs/ardour/playlist.cc

@@ -587,6 +587,7 @@ Playlist::notify_region_added (boost::shared_ptr<Region> r)
 		pending_contents_change = false;
 		RegionAdded (boost::weak_ptr<Region> (r)); /* EMIT SIGNAL */
 		ContentsChanged ();                        /* EMIT SIGNAL */
+		RegionFactory::CheckNewRegion (r);         /* EMIT SIGNAL */
 	}
 }
 
@@ -655,6 +656,7 @@ Playlist::flush_notifications (bool from_undo)
 	for (s = pending_adds.begin (); s != pending_adds.end (); ++s) {
 		(*s)->clear_changes ();
 		RegionAdded (boost::weak_ptr<Region> (*s)); /* EMIT SIGNAL */
+		RegionFactory::CheckNewRegion (*s);         /* EMIT SIGNAL */
 	}
 
 	if ((regions_changed && !in_set_state) || pending_layering) {