Bug 31785: Fix for adding non-public library

Bug 31785: Fix for adding non-public library

The code in admin/branches.pl changed a 0 to undef which is not
desirable for booleans.
A similar fix was already present for pickup_location.
This may need a bit more thought (somewhere else!).

Test plan:
Add a new branch with pickup location No, public No.
Check.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>