### 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
window->set_theme(theme);
			}
			OS::get_singleton()->set_low_processor_usage_mode_sleep_usec(int(EDITOR_GET("interface/editor/low_processor_mode_sleep_usec")));
			get_tree()->get_root()->set_as_audio_listener_3d(false);
			get_tree()->get_root()->set_as_audio_listener_2d(false);
			get_tree()->get_root()->set_snap_2d_transforms_to_pixel(false);
			get_tree()->get_root()->set_snap_2d_vertices_to_pixel(false);
			get_tree()->set_auto_accept_quit(false);
#ifdef ANDROID_ENABLED
			get_tree()->set_quit_on_go_back(false);
#endif
			get_tree()->get_root()->connect("files_dropped", callable_mp(this, &EditorNode::_dropped_files));
			command_palette->register_shortcuts_as_command();
			MessageQueue::get_singleton()->push_callable(callable_mp(this, &EditorNode::_begin_first_scan));
			
		} break;
		case NOTIFICATION_EXIT_TREE: {
			if (progress_dialog) {
				progress_dialog->queue_free();
			}
			if (load_error_dialog) {
				load_error_dialog->queue_free();
			}
			if (execute_output_dialog) {
				execute_output_dialog->queue_free();
			}
			if (warning) {
				warning->queue_free();
			}
			if (accept) {