### 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
EditorFileSystemDirectory *efsd = EditorFileSystem::get_singleton()->get_filesystem_path(p_path.get_base_dir());
	if (efsd) {
		String file = p_path.get_file();
		for (int i = 0; i < efsd->get_file_count(); i++) {
			if (efsd->get_file(i) == file) {
				String type = efsd->get_file_type(i);
				if (singleton->icon_type_cache.has(type)) {
					return singleton->icon_type_cache[type];
				} else {
					return singleton->icon_type_cache["Object"];
				}
			}
		}
	}
	return singleton->icon_type_cache["Object"];
}
void EditorNode::_build_icon_type_cache() {