### 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)

add_type_options->clear();
	List<StringName> names;
	ThemeDB::get_singleton()->get_default_theme()->get_type_list(&names);
	if (include_own_types) {
		edited_theme->get_type_list(&names);
	}
	names.sort_custom<StringName::AlphCompare>();
	Vector<StringName> unique_names;
	for (const StringName &E : names) {
		
		if (!p_filter.is_subsequence_ofn(String(E))) {
			continue;
		}
		
		if (unique_names.has(E)) {
			continue;
		}
		unique_names.append(E);
		Ref<Texture2D> item_icon;
		if (E == "") {
			item_icon = get_theme_icon(SNAME("NodeDisabled"), SNAME("EditorIcons"));
		} else {
			item_icon = EditorNode::get_singleton()->get_class_icon(E, "NodeDisabled");
		}
		add_type_options->add_item(E, item_icon);
	}
}
void ThemeTypeDialog::_add_type_filter_cbk(const String &p_value) {