Bug 24966: (QA follow-up) Fix return value of hold_patron_bcode

Bug 24966: (QA follow-up) Fix return value of hold_patron_bcode

It is used in list context, but we need a scalar value.
Can be fixed by adding scalar's, or returning empty string as here.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Joy Nelson <joy@bywatersolutions.com>
(cherry picked from commit 48d42a68794c3bf85c087adf2185d979929a13bc)

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>