CORE-5180 manually call first scroll for idx item seqs

scroll queries of search type scan don't return the first set of matches like ones of other search types do.  This causes the clojurewerkz.elastisch.rest.document/scroll-seq call to fail.  To fix this problem, the The first call to clojurewerkz.elastisch.rest.document/scroll is performed manually before passing the result to scroll-seq.