### Godot version

v4.0.beta17.mono.official [c40020513]

### System information

Window 11, Forward+, GTX 1060

### Issue description

Adding two theme variations in a row result to a  crash.

https://user-images.githubusercontent.com/93253123/217037249-1ce1d56d-beb6-4435-83ad-9f8a07fe0e96.mp4



### Steps to reproduce

1. Create a project.
2. Create a theme.
3. Double click to go in the theme editor.
4. Click on manage items buttons.
5. In the add type field type a name to add a type.
6. type another name to add a second type.
7. Crash.

### Minimal reproduction project

[ThemeVariationCrash.zip](https://github.com/godotengine/godot/files/10665863/ThemeVariationCrash.zip)

current_focusable = property_focusable;
		}
	}
	_clear();
	if (!object) {
		return;
	}
	List<Ref<EditorInspectorPlugin>> valid_plugins;
	for (int i = inspector_plugin_count - 1; i >= 0; i--) { 
		if (!inspector_plugins[i]->can_handle(object)) {
			continue;
		}
		valid_plugins.push_back(inspector_plugins[i]);
	}
	
	
	bool draw_warning = false;
	bool all_read_only = false;
	if (is_inside_tree()) {
		if (object->has_method("_is_read_only")) {
			all_read_only = object->call("_is_read_only");
		}
		Node *nod = Object::cast_to<Node>(object);
		Node *es = EditorNode::get_singleton()->get_edited_scene();
		if (nod && es != nod && nod->get_owner() != es) {
			
			
			draw_warning = true;
		} else {
			if (!all_read_only) {