### 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)

undo_redo->add_do_method(this, "_edit_request_change", object, "");
			undo_redo->add_undo_method(this, "_edit_request_change", object, "");
		} else {
			undo_redo->add_do_method(this, "_edit_request_change", object, p_name);
			undo_redo->add_undo_method(this, "_edit_request_change", object, p_name);
		}
		Resource *r = Object::cast_to<Resource>(object);
		if (r) {
			if (String(p_name) == "resource_local_to_scene") {
				bool prev = object->get(p_name);
				bool next = p_value;
				if (next) {
					undo_redo->add_do_method(r, "setup_local_to_scene");
				}
				if (prev) {
					undo_redo->add_undo_method(r, "setup_local_to_scene");
				}
			}
		}
		undo_redo->add_do_method(this, "emit_signal", _prop_edited, p_name);
		undo_redo->add_undo_method(this, "emit_signal", _prop_edited, p_name);
		undo_redo->commit_action();
	}
	if (editor_property_map.has(p_name)) {
		for (EditorProperty *E : editor_property_map[p_name]) {
			E->update_editor_property_status();
		}
	}
}
bool EditorInspector::_is_main_editor_inspector() const {