(2) Where a foreign bill, appearing on the face of it to be such, has been dishonoured by non-acceptance, it must be duly protested for non-acceptance, and where such a bill, which has not been previously dishonoured by non-acceptance, is dishonoured by non-payment, it must be duly protested for non-payment. If it be not so protested, the drawer and the indorsers are discharged. Where a bill does not appear on the face of it to be a foreign bill, protest thereof in case of dishonour is unnecessary.