No lands declared forfeited to the United States by sections 904 to 907 of this title shall by reason of such forfeiture inure to the benefit of any State or corporation to which lands may have been granted by Congress, except as therein otherwise provided; nor shall said sections be construed to enlarge the area of land originally covered by any such grant, or to confer any right upon any State, corporation, or person to lands which were excepted from such grant. Nor shall the moiety of the lands granted to any railroad company on account of a main and a branch line appertaining to uncompleted road, and forfeited by section 904 of this title, within the conflicting limits of the grants for such main and branch lines, when but one of such lines has been completed, inure by virtue of the forfeiture declared to the benefit of the completed line.