### 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)

if (updating_tree) {
		return;
	}
	updating_tree = true;
	TreeItem *root = import_items_tree->get_root();
	_select_all_subitems(root, false);
	updating_tree = false;
}
void ThemeItemImportTree::_select_full_items_pressed() {
	if (updating_tree) {
		return;
	}
	updating_tree = true;
	TreeItem *root = import_items_tree->get_root();
	_select_all_subitems(root, true);
	updating_tree = false;
}
void ThemeItemImportTree::_deselect_all_items_pressed() {
	if (updating_tree) {
		return;
	}
	updating_tree = true;
	TreeItem *root = import_items_tree->get_root();
	_deselect_all_subitems(root, true);
	updating_tree = false;
}
void ThemeItemImportTree::_select_all_data_type_pressed(int p_data_type) {