When sorting a search results set the isFilterSort variable is passed

When sorting a search results set the isFilterSort variable is passed
to searchBarSubmit.  In side searchBarSumbit there is a call to the
opac_utils.js function clearSearchParams function.  This removes all
search paramaters when sorting a result set, which is not the desired
effect.  I have wraped clearSearchParams in a check to make sure
isFilterSort is not set before calling the clearSearchParams function,
and this check ensures that the current search's paramaters are passed
to sort operations.

Signed-off-by: Liam Whalen <lwhalen@evergreen-dev.catalogue.nrcan.gc.ca>
Signed-off-by: Jason Stephenson <jason@sigio.com>