### 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
distraction_free->set_toggle_mode(true);
	tabbar_container->add_child(distraction_free);
	scene_root_parent = memnew(PanelContainer);
	scene_root_parent->set_custom_minimum_size(Size2(0, 80) * EDSCALE);
	scene_root_parent->add_theme_style_override("panel", gui_base->get_theme_stylebox(SNAME("Content"), SNAME("EditorStyles")));
	scene_root_parent->set_draw_behind_parent(true);
	srt->add_child(scene_root_parent);
	scene_root_parent->set_v_size_flags(Control::SIZE_EXPAND_FILL);
	scene_root = memnew(SubViewport);
	scene_root->set_embedding_subwindows(true);
	scene_root->set_disable_3d(true);
	scene_root->set_disable_input(true);
	scene_root->set_as_audio_listener_2d(true);
	main_screen_vbox = memnew(VBoxContainer);
	main_screen_vbox->set_name("MainScreen");
	main_screen_vbox->set_v_size_flags(Control::SIZE_EXPAND_FILL);
	main_screen_vbox->add_theme_constant_override("separation", 0);
	scene_root_parent->add_child(main_screen_vbox);
	bool global_menu = !bool(EDITOR_GET("interface/editor/use_embedded_menu")) && DisplayServer::get_singleton()->has_feature(DisplayServer::FEATURE_GLOBAL_MENU);
	bool can_expand = bool(EDITOR_GET("interface/editor/expand_to_title")) && DisplayServer::get_singleton()->has_feature(DisplayServer::FEATURE_EXTEND_TO_TITLE);
	if (can_expand) {
		
		left_menu_spacer = memnew(Control);
		left_menu_spacer->set_mouse_filter(Control::MOUSE_FILTER_PASS);
		title_bar->add_child(left_menu_spacer);
	}
	main_menu = memnew(MenuBar);
	title_bar->add_child(main_menu);
	main_menu->add_theme_style_override("hover", gui_base->get_theme_stylebox(SNAME("MenuHover"), SNAME("EditorStyles")));
	main_menu->set_flat(true);