### 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)

HBoxContainer *top_menu = memnew(HBoxContainer);
	add_child(top_menu);
	theme_name = memnew(Label);
	theme_name->set_text(TTR("Theme:"));
	theme_name->set_theme_type_variation("HeaderSmall");
	top_menu->add_child(theme_name);
	top_menu->add_spacer(false);
	Button *theme_save_button = memnew(Button);
	theme_save_button->set_text(TTR("Save"));
	theme_save_button->set_flat(true);
	theme_save_button->connect("pressed", callable_mp(this, &ThemeEditor::_theme_save_button_cbk).bind(false));
	top_menu->add_child(theme_save_button);
	Button *theme_save_as_button = memnew(Button);
	theme_save_as_button->set_text(TTR("Save As..."));
	theme_save_as_button->set_flat(true);
	theme_save_as_button->connect("pressed", callable_mp(this, &ThemeEditor::_theme_save_button_cbk).bind(true));
	top_menu->add_child(theme_save_as_button);
	top_menu->add_child(memnew(VSeparator));
	Button *theme_edit_button = memnew(Button);
	theme_edit_button->set_text(TTR("Manage Items..."));