### 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
while (!eta.done.is_set()) {
		{
			MutexLock lock(eta.execute_output_mutex);
			if (prev_len != eta.output.length()) {
				String to_add = eta.output.substr(prev_len, eta.output.length());
				prev_len = eta.output.length();
				execute_outputs->add_text(to_add);
				DisplayServer::get_singleton()->process_events(); 
				Main::iteration();
			}
		}
		OS::get_singleton()->delay_usec(1000);
	}
	eta.execute_output_thread.wait_to_finish();
	execute_outputs->add_text("\nExit Code: " + itos(eta.exitcode));
	if (execute_output_dialog) {
		if (p_close_on_errors && eta.exitcode != 0) {
			execute_output_dialog->hide();
		}
		if (p_close_on_ok && eta.exitcode == 0) {
			execute_output_dialog->hide();
		}
		execute_output_dialog->get_ok_button()->set_disabled(false);
	}
	return eta.exitcode;
}
void EditorNode::notify_settings_changed() {
	settings_changed = true;
}
EditorNode::EditorNode() {