### Godot version

4.1 rc3

### System information

Windows 10.0.19045 - Vulkan (Forward+) - dedicated NVIDIA GeForce GTX 1060 (NVIDIA; 30.0.15.1403) - Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz (8 Threads)

### Issue description

This™
![image](https://github.com/godotengine/godot/assets/2223172/cb33110f-a5b0-400a-951f-3fa425f05714)

It can still happen, but it's more difficult to trigger.

### Steps to reproduce

1. Create a new scene with a Control node
2. Add Theme to the Control
3. Open Theme Editor
4. Clear the `theme` property in Control
5. Save, with Theme Editor opened
6. Restart

### Minimal reproduction project

N/A
exiting = true;
	if (project_run_bar->is_playing()) {
		project_run_bar->stop_playing();
	}
	String to_reopen;
	if (get_tree()->get_edited_scene_root()) {
		to_reopen = get_tree()->get_edited_scene_root()->get_scene_file_path();
	}
	_exit_editor(EXIT_SUCCESS);
	List<String> args;
	for (const String &a : Main::get_forwardable_cli_arguments(Main::CLI_SCOPE_TOOL)) {
		args.push_back(a);
	}
	args.push_back("--path");
	args.push_back(ProjectSettings::get_singleton()->get_resource_path());
	args.push_back("-e");
	if (!to_reopen.is_empty()) {
		args.push_back(to_reopen);
	}
	OS::get_singleton()->set_restart_on_exit(true, args);
}
void EditorNode::_save_all_scenes() {