### 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
update_spinner->set_visible(EDITOR_GET("interface/editor/show_update_spinner"));
	const bool update_continuously = EDITOR_GET("interface/editor/update_continuously");
	PopupMenu *update_popup = update_spinner->get_popup();
	update_popup->set_item_checked(update_popup->get_item_index(SETTINGS_UPDATE_CONTINUOUSLY), update_continuously);
	update_popup->set_item_checked(update_popup->get_item_index(SETTINGS_UPDATE_WHEN_CHANGED), !update_continuously);
	if (update_continuously) {
		update_spinner->set_tooltip_text(TTR("Spins when the editor window redraws.\nUpdate Continuously is enabled, which can increase power usage. Click to disable it."));
		
		
		
		
		const bool dark_theme = EditorSettings::get_singleton()->is_dark_theme();
		update_spinner->set_self_modulate(
				gui_base->get_theme_color(SNAME("error_color"), SNAME("Editor")) * (dark_theme ? Color(1.1, 1.1, 1.1) : Color(4.25, 4.25, 4.25)));
	} else {
		update_spinner->set_tooltip_text(TTR("Spins when the editor window redraws."));
		update_spinner->set_self_modulate(Color(1, 1, 1));
	}
	OS::get_singleton()->set_low_processor_usage_mode(!update_continuously);
}
void EditorNode::_on_plugin_ready(Object *p_script, const String &p_activate_name) {