### 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)

_update_add_type_options(p_value);
}
void ThemeTypeDialog::_add_type_options_cbk(int p_index) {
	add_type_filter->set_text(add_type_options->get_item_text(p_index));
}
void ThemeTypeDialog::_add_type_dialog_entered(const String &p_value) {
	_add_type_selected(p_value.strip_edges());
}
void ThemeTypeDialog::_add_type_dialog_activated(int p_index) {
	_add_type_selected(add_type_options->get_item_text(p_index));
}
void ThemeTypeDialog::_add_type_selected(const String &p_type_name) {
	pre_submitted_value = p_type_name;
	if (p_type_name.is_empty()) {
		add_type_confirmation->popup_centered();
		return;
	}
	_add_type_confirmed();
}
void ThemeTypeDialog::_add_type_confirmed() {