Bug 23329: (QA follow-up) Resolve warning on wrong biblionumber

Bug 23329: (QA follow-up) Resolve warning on wrong biblionumber

Passing a wrong biblionumber generates a warning:
    GetMarcUrls called on undefined record at opac/tracklinks.pl line 58.

Test plan:
[1] Try it again with a wrong biblionumber and check the logs.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>