Provided That nothing in this Act contained, shall make void any Grant of any Quitt-Rents, or other Rents made in Consideration of any just Debt or Debts released to the Crowne, to the full Value of such Grant, or make void any Grant for Reduction or Abatement of any Quitt-rent, where such Abatement hath beene made in Consideration of the Barrennesse or Coursenesse of any Lands out of which such Quitt-Rents are issueing, or for their better Habitation or Improvement.