Fix crash on FileSystemDock's tree when trying to collapse or expand folder

(cherry picked from commit e6145027efb4ad0a5615477c8df13761063c6157)

editor/filesystem_dock.cpp

@@ -74,6 +74,9 @@ bool FileSystemDock::_create_tree(TreeItem *p_parent, EditorFileSystemDirectory
 	subdirectory_item->set_metadata(0, lpath);
 	if (!p_select_in_favorites && (path == lpath || ((display_mode == DISPLAY_MODE_SPLIT) && path.get_base_dir() == lpath))) {
 		subdirectory_item->select(0);
+		// Keep select an item when re-created a tree
+		// To prevent crashing when nothing is selected.
+		subdirectory_item->set_as_cursor(0);
 	}
 
 	if (p_unfold_path && path.begins_with(lpath) && path != lpath) {