Fix save/restore of Insert-At position

UIConfig insert-at-position saves/restores the enum as integer.
This is used directly as parameter for insert_at_combo.set_active().
For this to work, the enum needs to match the order of elements
in the dropdown.

It would be preferable to register the enum, and map the
dropdown entries, but for now this does the trick, without
breaking existing UIConfigs.

gtk2_ardour/add_route_dialog.cc

@@ -165,6 +165,7 @@ AddRouteDialog::AddRouteDialog ()
 		     );
 	}
 
+	/* order needs to match enum InsertAt */
 	insert_at_combo.append (_("First"));
 	insert_at_combo.append (_("Before Selection"));
 	insert_at_combo.append (_("After Selection"));

gtk2_ardour/route_dialogs.h

@@ -22,9 +22,9 @@
 namespace RouteDialogs {
 
 enum InsertAt {
+	First,
 	BeforeSelection,
 	AfterSelection,
-	First,
 	Last
 };