Fix typo which caused popup to display on incorrect coordinates.

editor/filesystem_dock.cpp

@@ -1101,7 +1101,7 @@ void FileSystemDock::_dir_rmb_pressed(const Vector2 &p_pos) {
 	folder_options->add_item(TTR("Expand all"), FOLDER_EXPAND_ALL);
 	folder_options->add_item(TTR("Collapse all"), FOLDER_COLLAPSE_ALL);
 
-	folder_options->set_pos(files->get_global_pos() + p_pos);
+	folder_options->set_pos(tree->get_global_pos() + p_pos);
 	folder_options->popup();
 }