### 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)

}
			_add_focusable(item_editor);
			icon_items_list->add_child(item_control);
		}
	}
	
	{
		for (int i = stylebox_items_list->get_child_count() - 1; i >= 0; i--) {
			Node *node = stylebox_items_list->get_child(i);
			node->queue_free();
			stylebox_items_list->remove_child(node);
		}
		if (leading_stylebox.pinned) {
			HBoxContainer *item_control = _create_property_control(Theme::DATA_TYPE_STYLEBOX, leading_stylebox.item_name, true);
			EditorResourcePicker *item_editor = memnew(EditorResourcePicker);
			item_editor->set_h_size_flags(SIZE_EXPAND_FILL);
			item_editor->set_stretch_ratio(1.5);
			item_editor->set_base_type("StyleBox");
			Button *pin_leader_button = memnew(Button);
			pin_leader_button->set_flat(true);
			pin_leader_button->set_toggle_mode(true);
			pin_leader_button->set_pressed(true);
			pin_leader_button->set_icon(get_theme_icon(SNAME("Pin"), SNAME("EditorIcons")));
			pin_leader_button->set_tooltip_text(TTR("Unpin this StyleBox as a main style."));
			item_control->add_child(pin_leader_button);
			pin_leader_button->connect("pressed", callable_mp(this, &ThemeTypeEditor::_on_unpin_leader_button_pressed));
			item_control->add_child(item_editor);
			if (edited_theme->has_stylebox(leading_stylebox.item_name, edited_type)) {
				item_editor->set_edited_resource(leading_stylebox.stylebox);
			} else {