Надо поменять на
array( "where" => array( "id" => $product->get('resource_id'), ), "current" => 1, "showhidden" => 1, "showunpublished" => 1, )
А иначе корзина не работает.
array( "where" => array( "id" => $product->get('resource_id'), ), "current" => 1, "showhidden" => 1, "showunpublished" => 1, )