### 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)

include_own_types = p_enable;
}
ThemeTypeDialog::ThemeTypeDialog() {
	set_hide_on_ok(false);
	VBoxContainer *add_type_vb = memnew(VBoxContainer);
	add_child(add_type_vb);
	Label *add_type_filter_label = memnew(Label);
	add_type_filter_label->set_text(TTR("Filter the list of types or create a new custom type:"));
	add_type_vb->add_child(add_type_filter_label);
	add_type_filter = memnew(LineEdit);
	add_type_vb->add_child(add_type_filter);
	add_type_filter->connect("text_changed", callable_mp(this, &ThemeTypeDialog::_add_type_filter_cbk));
	add_type_filter->connect("text_submitted", callable_mp(this, &ThemeTypeDialog::_add_type_dialog_entered));
	Label *add_type_options_label = memnew(Label);
	add_type_options_label->set_text(TTR("Available Node-based types:"));
	add_type_vb->add_child(add_type_options_label);
	add_type_options = memnew(ItemList);
	add_type_options->set_v_size_flags(Control::SIZE_EXPAND_FILL);
	add_type_vb->add_child(add_type_options);
	add_type_options->connect("item_selected", callable_mp(this, &ThemeTypeDialog::_add_type_options_cbk));
	add_type_options->connect("item_activated", callable_mp(this, &ThemeTypeDialog::_add_type_dialog_activated));
	add_type_confirmation = memnew(ConfirmationDialog);
	add_type_confirmation->set_title(TTR("Type name is empty!"));
	add_type_confirmation->set_text(TTR("Are you sure you want to create an empty type?"));
	add_type_confirmation->connect("confirmed", callable_mp(this, &ThemeTypeDialog::_add_type_confirmed));
	add_child(add_type_confirmation);
}
VBoxContainer *ThemeTypeEditor::_create_item_list(Theme::DataType p_data_type) {