subcompositor: consider mapping after adding

ec8b49c93f calls subsurface_consider_map()
too early. Instead, call it after emitting new_subsurface signal to let
compositors receive a map event.

types/wlr_subcompositor.c

@@ -367,6 +367,7 @@ void subsurface_handle_parent_commit(struct wlr_subsurface *subsurface) {
 		subsurface->added = true;
 		wl_signal_emit_mutable(&subsurface->parent->events.new_subsurface,
 			subsurface);
+		subsurface_consider_map(subsurface, true);
 	}
 }
 
@@ -414,8 +415,6 @@ static struct wlr_subsurface *subsurface_create(struct wlr_surface *surface,
 
 	surface->role_data = subsurface;
 
-	subsurface_consider_map(subsurface, true);
-
 	return subsurface;
 }