Fix for WooCommerce 2+ for the ID property

As get_product() returns an instance of WC_Product the code expects the ID to be in uppercase ( due to it expecting an instance of WP_Post ).

This causes the property to not correct set as WC_Product's ID property is in lower case.

When the property isn't correct set it breaks the magic method __get ( which in turn stops the correct return values of calls to SKU or any other meta. Including updating stock ).