fix gridmap cursor showing the wrong mesh

(cherry picked from commit 726614ff4b0018379ed8fe1ea0461ba9403b671b)

modules/gridmap/grid_map_editor_plugin.cpp

@@ -938,6 +938,7 @@ void GridMapEditor::edit(GridMap *p_gridmap) {
 	}
 
 	update_palette();
+	_update_cursor_instance();
 
 	set_process(true);