### 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
return EditorNode::get_singleton()->get_edited_scene();
}
void EditorNode::_print_handler(void *p_this, const String &p_string, bool p_error, bool p_rich) {
	callable_mp_static(&EditorNode::_print_handler_impl).bind(p_string, p_error, p_rich).call_deferred();
}
void EditorNode::_print_handler_impl(const String &p_string, bool p_error, bool p_rich) {
	if (p_error) {
		singleton->log->add_message(p_string, EditorLog::MSG_TYPE_ERROR);
	} else if (p_rich) {
		singleton->log->add_message(p_string, EditorLog::MSG_TYPE_STD_RICH);
	} else {
		singleton->log->add_message(p_string, EditorLog::MSG_TYPE_STD);
	}
}
static void _execute_thread(void *p_ud) {