The 1892 RLDS edition accidentally dropped the repeated a here in 1 Nephi 16:38. This error has not continued in subsequent RLDS editions. Like the case of the repeated a before a conjoined adjective, the determiner (usually the indefinite article a) can be repeated when the two nouns king and ruler are conjoined. In one other case, there has been textual variation (see Jacob 1:9 in the following list), but the current LDS and RLDS texts now read correctly (and systematically) for all instances of conjoined king and ruler:
For further discussion, see conjunctive repetition in volume 3.
Summary: Maintain in 1 Nephi 16:38 the repeated indefinite article a for conjoined king and ruler.