[#33805] Only try to find a search page if the request Itemid is not a search page.

Also, find search pages by component id, not link string

Fixes this tracker item: http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=33805
Better safe than `Fatal error: Class 'JComponentHelper' not found` but, yes, it's hard to imagine how that class would not have been imported at this point.