Fix regression in scan & query after first page

Apologies, just spotted this when looking at reimplementing query & scan asynchronously - the implementations of `run1` in both bodies built a request based on the outer `opts` map, ignoring the passed-in `last-prim-kvs`, which would be different in subsequent invocations by `merge-more`.  Modified to merge the supplied value into `opts`.  It would have been correct only for single pages before, AFAICT.