Allow to initiate Rubberband-drag on blank Trackview

gtk2_ardour/editor_mouse.cc

@@ -1036,6 +1036,9 @@ Editor::button_press_handler_1 (ArdourCanvas::Item* item, GdkEvent* event, ItemT
 
 		case StreamItem:
 			/* in the past, we created a new midi region here, but perhaps that is best left to the Draw mode */
+			/* .. now we allow for rubberband selection (region gain) */
+			_drags->set (new EditorRubberbandSelectDrag (this, item), event);
+			return true;
 			break;
 
 		case AutomationTrackItem: