Bug 16958: Fix XSS in opac-imageviewer.pl

Bug 16958: Fix XSS in opac-imageviewer.pl

Test plan:
Trigger
/opac-imageviewer.pl?biblionumber=14&imagenumber=7"><sCrIpT>alert(42)<%2fsCrIpT>

=> Without this patch you will see the JS alert
=> With this patch applied you won't see it

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit 65918b146cd88f38a9d894be8175d049ea70d05f)
Signed-off-by: Frédéric Demians <f.demians@tamil.fr>