### 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_editor->set_edited_resource(Ref<Resource>());
			}
			item_editor->connect("resource_selected", callable_mp(this, &ThemeTypeEditor::_edit_resource_item));
			item_editor->connect("resource_changed", callable_mp(this, &ThemeTypeEditor::_stylebox_item_changed).bind(leading_stylebox.item_name));
			stylebox_items_list->add_child(item_control);
			stylebox_items_list->add_child(memnew(HSeparator));
		}
		HashMap<StringName, bool> stylebox_items = _get_type_items(edited_type, &Theme::get_stylebox_list, show_default);
		for (const KeyValue<StringName, bool> &E : stylebox_items) {
			if (leading_stylebox.pinned && leading_stylebox.item_name == E.key) {
				continue;
			}
			HBoxContainer *item_control = _create_property_control(Theme::DATA_TYPE_STYLEBOX, E.key, E.value);
			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");
			if (E.value) {
				if (edited_theme->has_stylebox(E.key, edited_type)) {
					item_editor->set_edited_resource(edited_theme->get_stylebox(E.key, edited_type));
				} else {
					item_editor->set_edited_resource(Ref<Resource>());
				}
				item_editor->connect("resource_selected", callable_mp(this, &ThemeTypeEditor::_edit_resource_item));
				item_editor->connect("resource_changed", callable_mp(this, &ThemeTypeEditor::_stylebox_item_changed).bind(E.key));
				Button *pin_leader_button = memnew(Button);
				pin_leader_button->set_flat(true);
				pin_leader_button->set_toggle_mode(true);
				pin_leader_button->set_icon(get_theme_icon(SNAME("Pin"), SNAME("EditorIcons")));
				pin_leader_button->set_tooltip_text(TTR("Pin this StyleBox as a main style. Editing its properties will update the same properties in all other StyleBoxes of this type."));