### 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)

item_remove_button->connect("pressed", callable_mp(this, &ThemeTypeEditor::_item_remove_cbk).bind(p_data_type, p_item_name));
		Button *item_rename_confirm_button = memnew(Button);
		item_rename_confirm_button->set_icon(get_theme_icon(SNAME("ImportCheck"), SNAME("EditorIcons")));
		item_rename_confirm_button->set_tooltip_text(TTR("Confirm Item Rename"));
		item_rename_confirm_button->set_flat(true);
		item_name_container->add_child(item_rename_confirm_button);
		item_rename_confirm_button->connect("pressed", callable_mp(this, &ThemeTypeEditor::_item_rename_confirmed).bind(p_data_type, p_item_name, item_name_container));
		item_rename_confirm_button->hide();
		Button *item_rename_cancel_button = memnew(Button);
		item_rename_cancel_button->set_icon(get_theme_icon(SNAME("ImportFail"), SNAME("EditorIcons")));
		item_rename_cancel_button->set_tooltip_text(TTR("Cancel Item Rename"));
		item_rename_cancel_button->set_flat(true);
		item_name_container->add_child(item_rename_cancel_button);
		item_rename_cancel_button->connect("pressed", callable_mp(this, &ThemeTypeEditor::_item_rename_canceled).bind(p_data_type, p_item_name, item_name_container));
		item_rename_cancel_button->hide();
	} else {
		item_name->add_theme_color_override("font_color", get_theme_color(SNAME("disabled_font_color"), SNAME("Editor")));
		Button *item_override_button = memnew(Button);
		item_override_button->set_icon(get_theme_icon(SNAME("Add"), SNAME("EditorIcons")));
		item_override_button->set_tooltip_text(TTR("Override Item"));
		item_override_button->set_flat(true);
		item_name_container->add_child(item_override_button);
		item_override_button->connect("pressed", callable_mp(this, &ThemeTypeEditor::_item_override_cbk).bind(p_data_type, p_item_name));
	}
	return item_control;
}
void ThemeTypeEditor::_add_focusable(Control *p_control) {
	focusables.append(p_control);
}
void ThemeTypeEditor::_update_type_items() {