Every transfer of any such mortgage heretofore made by indorsement shall be, and be deemed to have been, as valid as if this Act had been in force at the date of such transfer; and no stamp-duty shall be, or be deemed to have been, chargeable in respect of any such transfer; and no penalty shall be deemed to have been incurred by reason of any failure to comply with the provisions of the said section 255 or of the law relating to stamp-duties for the time being in force.