### 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
String path = p_resource->get_path();
	if (path.is_resource_file() && !FileAccess::exists(path + ".import")) {
		save_resource_in_path(p_resource, p_resource->get_path());
	} else {
		save_resource_as(p_resource);
	}
}
void EditorNode::save_resource_as(const Ref<Resource> &p_resource, const String &p_at_path) {
	{
		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 (!get_edited_scene() || get_edited_scene()->get_scene_file_path() != base) {
					show_warning(TTR("This resource can't be saved because it does not belong to the edited scene. Make it unique first."));
					return;
				}
			}
		} else {
			if (FileAccess::exists(path + ".import")) {
				show_warning(TTR("This resource can't be saved because it was imported from another file. Make it unique first."));
				return;
			}