21. If any letters of administration granted to the Administrator General in accordance with the provisions of this Act are revoked, upon the grant of probate of a will, or upon the grant of letters of administration with a copy of the will annexed, all payments made or acts done by or under the authority of the Administrator General in pursuance of such letters administration, prior to the revocation, which would have been valid under any letters of administration lawfully granted to him with a copy of such will annexed, shall be deemed valid notwithstanding such revocation.