If, upon the trial of said issue, it shall be decided that the will or a part of it is for any reason invalid, or that it is not sufficiently proved to have been the last will of the testator, the will or part and probate thereof shall be annulled and revoked and to that extent the powers of the personal representative shall cease, but the personal representative shall not be liable for any act done in good faith previous to such annulling or revoking.