The original text reads as a resultive clause. The change to and first appeared in the 1837 edition and was not marked by Joseph Smith in the printer’s manuscript, so this change may simply be a typo. The resultive that more accurately represents the semantic connection between the two clauses.
There has been a tendency to replace the resultive that elsewhere in the text. Typically we expect so that rather than that, with the result that when only that occurs, there is a tendency to substitute and. For other examples of this change, see under 1 Nephi 13:15, 1 Nephi 15:34, Jacob 4:11, Alma 32:5, 3 Nephi 3:26, Ether 8:11, Ether 12:14, and Ether 14:30.
Summary: Restore the resultive that in 1 Nephi 11:29 (“that I saw them not”).