### 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)

Ref<InputEventKey> k = p_event;
	if (k.is_valid()) {
		if (!k->is_pressed()) {
			return;
		}
		switch (k->get_keycode()) {
			case Key::KP_ENTER:
			case Key::ENTER: {
				_confirm_edit_theme_item();
				edit_theme_item_dialog->hide();
				edit_theme_item_dialog->set_input_as_handled();
			} break;
			case Key::ESCAPE: {
				edit_theme_item_dialog->hide();
				edit_theme_item_dialog->set_input_as_handled();
			} break;
			default:
				break;
		}
	}
}
void ThemeItemEditorDialog::_open_select_another_theme() {