### 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)

edited_theme->get_stylebox_type_list(&types);
		for (const StringName &E : types) {
			names.clear();
			edited_theme->get_stylebox_list(E, &names);
			for (const StringName &F : names) {
				if (stylebox_item == edited_theme->get_stylebox(F, E)) {
					belongs_to_theme = true;
					break;
				}
			}
		}
	} else if (Object::cast_to<Texture2D>(p_node)) {
		Ref<Texture2D> icon_item = Object::cast_to<Texture2D>(p_node);
		List<StringName> types;
		List<StringName> names;
		edited_theme->get_icon_type_list(&types);
		for (const StringName &E : types) {
			names.clear();
			edited_theme->get_icon_list(E, &names);
			for (const StringName &F : names) {
				if (icon_item == edited_theme->get_icon(F, E)) {
					belongs_to_theme = true;
					break;
				}
			}
		}
	}
	return belongs_to_theme;
}
void ThemeEditorPlugin::make_visible(bool p_visible) {