Bug 17526: Change grep to deal with malformed sortfield

Bug 17526: Change grep to deal with malformed sortfield

Giving sortfield a malformed value when viewing lists results in
Internal Server Error.

eg.
http://localhost:8080/cgi-bin/koha/opac-shelves.pl?op=view&shelfnumber=1&sortfield=title(

Note the trailing (

Before Patch: kaboom
apply patch
restart
After Patch: No kaboom

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>