### 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
Ref<DirAccess> dir = DirAccess::create(DirAccess::ACCESS_FILESYSTEM);
	for (int i = 0; i < p_files.size(); i++) {
		String from = p_files[i];
		String to = to_path.path_join(from.get_file());
		if (dir->dir_exists(from)) {
			Vector<String> sub_files;
			Ref<DirAccess> sub_dir = DirAccess::open(from);
			sub_dir->list_dir_begin();
			String next_file = sub_dir->get_next();
			while (!next_file.is_empty()) {
				if (next_file == "." || next_file == "..") {
					next_file = sub_dir->get_next();
					continue;
				}
				sub_files.push_back(from.path_join(next_file));
				next_file = sub_dir->get_next();
			}
			if (!sub_files.is_empty()) {
				dir->make_dir(to);
				_add_dropped_files_recursive(sub_files, to);
			}
			continue;
		}
		dir->copy(from, to);
	}
}
void EditorNode::_file_access_close_error_notify(const String &p_str) {