Make autosuggest view bail out with an error message when no partial
title is included in the querystring.

This (hopefully) solves some memory issues -- we've been seeing a lot
of intermittent cases of this view being hit with no search term, and
eventually hitting a MemoryError.
Merge pull request #1229 from ubernostrum/autosuggest-bail-out

Make autosuggest view bail out on bad querystring