Bug 20982: Sanitize category to prevent XSS on opac-shelves.pl

== Test plan ==
1. Go to http://localhost:8080/cgi-bin/koha/opac-shelves.pl?category=function(){window.location.href%20=%20%27https://git.koha-community.org/stats/koha-master/authors.html%27}()
2. Note that you are redirected to another website
3. Apply the patch & restart services
4. Repeat the above and you are not redirected

Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>

Signed-off-by: David Cook <dcook@prosentient.com.au>

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>

koha-tmpl/opac-tmpl/bootstrap/en/modules/opac-shelves.tt

@@ -1096,7 +1096,7 @@ function AdjustRemark() {
     if( $("#category").length > 0 ) {
         category = $("#category").val();
     } else {
-        category = [% category | html %];
+        category = "[% category | html %]";
     }
     var perms = $("#allow_changes_from").val();
 

opac/opac-shelves.pl

@@ -434,7 +434,7 @@ $template->param(
     referer  => $referer,
     shelf    => $shelf,
     messages => \@messages,
-    category => $category,
+    category => ($category == 1 || $category == 2) ? $category : "",
     print    => scalar $query->param('print') || 0,
     listsview => 1,
 );