### 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)

}
			has_any_items = true;
		}
	}
	
	TreeItem *selected_item = edit_type_list->get_selected();
	if (selected_item) {
		if (!has_any_items) {
			edit_items_message->set_text(TTR("This theme type is empty.\nAdd more items to it manually or by importing from another theme."));
			edit_items_message->show();
		} else {
			edit_items_message->set_text("");
			edit_items_message->hide();
		}
	}
}
void ThemeItemEditorDialog::_item_tree_button_pressed(Object *p_item, int p_column, int p_id, MouseButton p_button) {
	if (p_button != MouseButton::LEFT) {
		return;
	}
	TreeItem *item = Object::cast_to<TreeItem>(p_item);
	if (!item) {
		return;
	}
	switch (p_id) {
		case ITEMS_TREE_RENAME_ITEM: {
			String item_name = item->get_text(0);
			int data_type = item->get_parent()->get_metadata(0);
			_open_rename_theme_item_dialog((Theme::DataType)data_type, item_name);
			_update_edit_item_tree(edited_item_type);