### 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
List<String> scenes;
	int current_tab = scene_tabs->get_current_tab();
	for (int i = 0; i < p_resources.size(); i++) {
		String file_type = ResourceLoader::get_resource_type(p_resources[i]);
		if (file_type == "PackedScene") {
			scenes.push_back(p_resources[i]);
			
			continue;
		}
		if (!ResourceCache::has(p_resources[i])) {
			
			continue;
		}
		
		Ref<Resource> resource = ResourceCache::get_ref(p_resources[i]);
		if (resource.is_valid()) {
			resource->reload_from_file();
		}
	}
	for (const String &E : scenes) {
		reload_scene(E);
		reload_instances_with_path_in_edited_scenes(E);
	}
	scene_tabs->set_current_tab(current_tab);
}
void EditorNode::_sources_changed(bool p_exist) {