### 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
install_android_build_template->popup_centered();
				} else {
					gradle_build_manage_templates->popup_centered();
				}
			}
		} break;
		case TOOLS_BUILD_PROFILE_MANAGER: {
			build_profile_manager->popup_centered_clamped(Size2(700, 800) * EDSCALE, 0.8);
		} break;
		case RUN_USER_DATA_FOLDER: {
			
			OS::get_singleton()->ensure_user_data_dir();
			OS::get_singleton()->shell_show_in_file_manager(OS::get_singleton()->get_user_data_dir(), true);
		} break;
		case FILE_EXPLORE_ANDROID_BUILD_TEMPLATES: {
			OS::get_singleton()->shell_show_in_file_manager(ProjectSettings::get_singleton()->get_resource_path().path_join("android"), true);
		} break;
		case FILE_QUIT:
		case RUN_PROJECT_MANAGER:
		case RELOAD_CURRENT_PROJECT: {
			if (!p_confirmed) {
				bool save_each = EDITOR_GET("interface/editor/save_each_scene_on_quit");
				if (_next_unsaved_scene(!save_each) == -1) {
					if (EditorUndoRedoManager::get_singleton()->is_history_unsaved(EditorUndoRedoManager::GLOBAL_HISTORY)) {
						if (p_option == RELOAD_CURRENT_PROJECT) {
							save_confirmation->set_ok_button_text(TTR("Save & Reload"));
							save_confirmation->set_text(TTR("Save modified resources before reloading?"));
						} else {
							save_confirmation->set_ok_button_text(TTR("Save & Quit"));
							save_confirmation->set_text(TTR("Save modified resources before closing?"));