Section 12.  Whenever any immovable property has been forfeited or adjudicated to the state for nonpayment of taxes due prior to January 1, 1880, and the state did not sell or dispose of it or dispossess the tax debtor or his heirs, successors, or assigns prior to the adoption of the Constitution of 1921, it shall be presumed conclusively that the forfeiture or adjudication was irregular and null or that the property has been redeemed.  The state and its assigns shall be estopped forever from claiming any title to the property because of such forfeiture or adjudication.