Membership options page fatal error

In case if assigned to membership product was deleted, it will cause fatal error on product select box output.

Fix:

wp-content/plugins/yith-woocommerce-membership/includes/class.ajax-products-field.php : 96-100

if ( $option_value != '' && get_post( $option_value ) ) {
    $product       = wc_get_product( $option_value );
    $data_selected = wp_kses_post( $product->get_formatted_name() );
    $value         = $option_value;
}