### 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)

select_all_items_tooltip = TTR("Select all visible font items.");
				select_full_items_tooltip = TTR("Select all visible font items and their data.");
				deselect_all_items_tooltip = TTR("Deselect all visible font items.");
				break;
			case Theme::DATA_TYPE_FONT_SIZE:
				select_items_icon = select_font_sizes_icon;
				select_items_label = select_font_sizes_label;
				deselect_all_items_button = deselect_all_font_sizes_button;
				select_all_items_button = select_all_font_sizes_button;
				select_full_items_button = select_full_font_sizes_button;
				total_selected_items_label = total_selected_font_sizes_label;
				items_title = TTR("Font sizes");
				select_all_items_tooltip = TTR("Select all visible font size items.");
				select_full_items_tooltip = TTR("Select all visible font size items and their data.");
				deselect_all_items_tooltip = TTR("Deselect all visible font size items.");
				break;
			case Theme::DATA_TYPE_ICON:
				select_items_icon = select_icons_icon;
				select_items_label = select_icons_label;
				deselect_all_items_button = deselect_all_icons_button;
				select_all_items_button = select_all_icons_button;
				select_full_items_button = select_full_icons_button;
				total_selected_items_label = total_selected_icons_label;
				items_title = TTR("Icons");
				select_all_items_tooltip = TTR("Select all visible icon items.");
				select_full_items_tooltip = TTR("Select all visible icon items and their data.");
				deselect_all_items_tooltip = TTR("Deselect all visible icon items.");
				break;
			case Theme::DATA_TYPE_STYLEBOX:
				select_items_icon = select_styleboxes_icon;