Fix PluginListChanged() emission order

This is only relevant when manually scanning plugins,
initiated from the UI thread. Call back (in same thread) needs
to happen after detecting ambiguities and refilling the info lists.

libs/ardour/plugin_manager.cc

@@ -566,7 +566,6 @@ PluginManager::refresh (bool cache_only)
 	}
 
 	BootMessage (_("Plugin Scan Complete..."));
-	PluginListChanged (); /* EMIT SIGNAL */
 	PluginScanMessage(X_("closeme"), "", false);
 	_cancel_scan = false;
 
@@ -609,6 +608,7 @@ PluginManager::refresh (bool cache_only)
 	detect_type_ambiguities (all_plugs);
 
 	save_scanlog ();
+	PluginListChanged (); /* EMIT SIGNAL */
 }
 
 void