It is the duty of the foreman of the grand jury to endorse on the indictment or, if it is a presentment, on the subpoena the names of the witnesses so sworn by the foreman and sign same officially, but the omission to endorse the names of those witnesses on the indictment or subpoena shall in no case invalidate the finding of the indictment or presentment, if the witnesses were, in point of fact, sworn by the foreman according to law.