### 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
ERR_FAIL_COND(!p_dock);
	Size2 borders = Size2(4, 4) * EDSCALE;
	
	Size2 dock_size = p_dock->get_size() + borders * 2;
	Point2 dock_screen_pos = p_dock->get_screen_position();
	int dock_index = p_dock->get_index() - 1;
	dock_slot[p_slot_index]->remove_child(p_dock);
	WindowWrapper *wrapper = memnew(WindowWrapper);
	wrapper->set_window_title(vformat(TTR("%s - Godot Engine"), p_dock->get_name()));
	wrapper->set_margins_enabled(true);
	gui_base->add_child(wrapper);
	wrapper->set_wrapped_control(p_dock);
	wrapper->set_meta("dock_slot", p_slot_index);
	wrapper->set_meta("dock_index", dock_index);
	wrapper->set_meta("dock_name", p_dock->get_name().operator String());
	wrapper->connect("window_close_requested", callable_mp(this, &EditorNode::_dock_floating_close_request).bind(wrapper));
	dock_select_popup->hide();
	if (p_show_window) {
		wrapper->restore_window(Rect2i(dock_screen_pos, dock_size), get_window()->get_current_screen());
	}
	_update_dock_containers();
	floating_docks.push_back(wrapper);
	_edit_current();
}
void EditorNode::_update_dock_containers() {