Nothing in sections three, four and five, or in the said orders, or in any sanad, shall be deemed to bar a suit for redemption,
        (a) where the instrument of mortgage was executed on or after the thirteenth day of February 1844 and fixed no term within which the property comprised therein might be redeemed, or
        (b) where the instrument of mortgage fixed a term within which the property comprised therein might be redeemed, and such term did not expire before the thirteenth day of February 1856.