### 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)

ERR_FAIL_COND(edited_theme.is_null());
	if (updating) {
		return;
	}
	updating = true;
	Control *focused = get_viewport()->gui_get_focus_owner();
	if (focused) {
		if (focusables.has(focused)) {
			
			updating = false;
			return;
		}
		Node *focus_parent = focused->get_parent();
		while (focus_parent) {
			Control *c = Object::cast_to<Control>(focus_parent);
			if (c && focusables.has(c)) {
				
				updating = false;
				return;
			}
			focus_parent = focus_parent->get_parent();
		}
	}
	List<StringName> theme_types;
	edited_theme->get_type_list(&theme_types);
	theme_types.sort_custom<StringName::AlphCompare>();
	theme_type_list->clear();
	if (theme_types.size() > 0) {
		theme_type_list->set_disabled(false);
		bool item_reselected = false;