### 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
load_scene(p_resource->get_path().get_slice("::", 0));
	InspectorDock::get_singleton()->call_deferred("edit_resource", p_resource);
}
bool EditorNode::is_resource_read_only(Ref<Resource> p_resource, bool p_foreign_resources_are_writable) {
	ERR_FAIL_COND_V(p_resource.is_null(), false);
	String path = p_resource->get_path();
	if (!path.is_resource_file()) {
		
		int srpos = path.find("::");
		if (srpos != -1) {
			String base = path.substr(0, srpos);
			
			if (ResourceLoader::get_resource_type(base) == "PackedScene") {
				if (!get_tree()->get_edited_scene_root() || get_tree()->get_edited_scene_root()->get_scene_file_path() != base) {
					
					
					if (!p_foreign_resources_are_writable || FileAccess::exists(base + ".import")) {
						return true;
					}
				}
			} else {
				
				if (FileAccess::exists(base + ".import")) {