Fixes a memory leak in FileSystemDock

Co-authored-by: Rafał Mikrut <[email protected]>

editor/filesystem_dock.cpp

@@ -140,6 +140,7 @@ bool FileSystemDock::_create_tree(TreeItem *p_parent, EditorFileSystemDirectory
 			subdirectory_item->set_collapsed(false);
 		} else if (dname != "res://") {
 			subdirectory_item->get_parent()->remove_child(subdirectory_item);
+			memdelete(subdirectory_item);
 		}
 	}