Bug 11329: Check for MARC record existence in catalogue/showmarc

Bug 11329: Check for MARC record existence in catalogue/showmarc

Intranet counterpart patch. Same check as in opac/opac-showmarc.

Test plan:
[1] Run showmarc.pl with valid biblionumber in id parameter.
[2] Remove id parameter from URL. You should get a 404 now.

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Passes koha-qa.pl, works as advertised.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>