A covenant by any such grantor "that he has done no act to encumber the said lands" shall have the same effect as if he covenanted that he had not done or executed, or knowingly suffered, any act, deed or thing whereby the lands and premises conveyed, or intended so to be, or any part thereof, are or will be charged, affected or encumbered in title, estate or otherwise.
Code 1919, § 5177.