Short circuit empty searches

Short circuit empty searches

If we have no search terms, we shouldn't kick off a search. Accordingly,
track whether we have, in fact, any type + value combos where value is
not an empty string, or a non-empty original query, and return
immediately if we have nothing to search.

Compare the results of the following opensrf call before and after:

request open-ils.search open-ils.search.biblio.multiclass.query {}
"title: "

Signed-off-by: Dan Scott <dscott@laurentian.ca>