### 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
export_template_manager->popup_manager();
		} break;
		case SETTINGS_MANAGE_FBX_IMPORTER: {
#if !defined(ANDROID_ENABLED) && !defined(WEB_ENABLED)
			fbx_importer_manager->show_dialog();
#endif
		} break;
		case SETTINGS_INSTALL_ANDROID_BUILD_TEMPLATE: {
			gradle_build_manage_templates->hide();
			file_android_build_source->popup_centered_ratio();
		} break;
		case SETTINGS_MANAGE_FEATURE_PROFILES: {
			feature_profile_manager->popup_centered_clamped(Size2(900, 800) * EDSCALE, 0.8);
		} break;
		case SETTINGS_TOGGLE_FULLSCREEN: {
			DisplayServer::get_singleton()->window_set_mode(DisplayServer::get_singleton()->window_get_mode() == DisplayServer::WINDOW_MODE_FULLSCREEN ? DisplayServer::WINDOW_MODE_WINDOWED : DisplayServer::WINDOW_MODE_FULLSCREEN);
		} break;
		case EDITOR_SCREENSHOT: {
			screenshot_timer->start();
		} break;
		case SETTINGS_PICK_MAIN_SCENE: {
			file->set_file_mode(EditorFileDialog::FILE_MODE_OPEN_FILE);
			List<String> extensions;
			ResourceLoader::get_recognized_extensions_for_type("PackedScene", &extensions);
			file->clear_filters();
			for (int i = 0; i < extensions.size(); i++) {
				file->add_filter("*." + extensions[i], extensions[i].to_upper());
			}
			Node *scene = editor_data.get_edited_scene_root();
			if (scene) {