### 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 (!add_meta_dialog) {
		add_meta_dialog = memnew(ConfirmationDialog);
		VBoxContainer *vbc = memnew(VBoxContainer);
		add_meta_dialog->add_child(vbc);
		HBoxContainer *hbc = memnew(HBoxContainer);
		vbc->add_child(hbc);
		hbc->add_child(memnew(Label(TTR("Name:"))));
		add_meta_name = memnew(LineEdit);
		add_meta_name->set_custom_minimum_size(Size2(200 * EDSCALE, 1));
		hbc->add_child(add_meta_name);
		hbc->add_child(memnew(Label(TTR("Type:"))));
		add_meta_type = memnew(OptionButton);
		for (int i = 0; i < Variant::VARIANT_MAX; i++) {
			if (i == Variant::NIL || i == Variant::RID || i == Variant::CALLABLE || i == Variant::SIGNAL) {
				continue; 
			}
			String type = i == Variant::OBJECT ? String("Resource") : Variant::get_type_name(Variant::Type(i));
			add_meta_type->add_icon_item(get_theme_icon(type, "EditorIcons"), type, i);
		}
		hbc->add_child(add_meta_type);
		add_meta_dialog->set_ok_button_text(TTR("Add"));
		add_child(add_meta_dialog);
		add_meta_dialog->register_text_enter(add_meta_name);
		add_meta_dialog->connect("confirmed", callable_mp(this, &EditorInspector::_add_meta_confirm));