Bug 35266: Fix biblio check in opac-MARCdetail

Bug 35266: Fix biblio check in opac-MARCdetail

We should check before retrieving metadata.

Test plan;
Try /cgi-bin/koha/opac-MARCdetail?biblionumber=X
Replace X by a not-existing biblionumber.
Verify that you get a 404 error page.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: David Nind <david@davidnind.com>
JD amended patch: Use ternary op

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>