Bug 16597: Fix XSS in opac-shareshelf

Bug 16597: Fix XSS in opac-shareshelf

To test
1/ Go to /cgi-bin/koha/opac-shareshelf.pl?op="><script>alert('XSS')</script>&shelfnumber=5
2/ Notice you see a js alert
3/ Apply patch
4/ It is gone

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 c47c835672a8fcd8c7df79663443f01639fc7657)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>