Bug 16597: Fix XSS in opac-shelves.pl

Bug 16597: Fix XSS in opac-shelves.pl

To test
1/ Hit /cgi-bin/koha/opac-shelves.pl?shelfnumber=5&category=1&op=edit_form&referer="><script>alert('XSS')</SCRIPT>
2/ Notice JS is executed
3/ Apply patch
4/ Notice it's fixed

This bug reported by

Alex Middleton at Dionach

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Brendan Gallagher <brendan@bywatersolutions.com>
(cherry picked from commit 344033c32490df3e396ed530dcbf250086483371)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>