It shall be the duty of all persons now holding or that may hereafter hold unexecuted land warrants, to file or enter the same with the surveyors of the proper district within two years after the passing of this act, or within two years after the date of such warrants respectively, and on failure thereof, such warrant or warrants shall not have any force or effect against a warrant of later date, nor against an actual settler on the lands called for in such unexecuted warrant.