### 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)

break;
		case Theme::DATA_TYPE_ICON:
			total_selected_items_label = total_selected_icons_label;
			break;
		case Theme::DATA_TYPE_STYLEBOX:
			total_selected_items_label = total_selected_styleboxes_label;
			break;
		case Theme::DATA_TYPE_MAX:
			return; 
	}
	if (!total_selected_items_label) {
		return;
	}
	int count = 0;
	for (const KeyValue<ThemeItem, ItemCheckedState> &E : selected_items) {
		ThemeItem ti = E.key;
		if (ti.data_type == p_data_type) {
			count++;
		}
	}
	if (count == 0) {
		total_selected_items_label->hide();
	} else {
		Array arr;
		arr.push_back(count);
		total_selected_items_label->set_text(TTRN("{num} currently selected", "{num} currently selected", count).format(arr, "{num}"));
		total_selected_items_label->show();
	}
}
void ThemeItemImportTree::_tree_item_edited() {