Bug 16942 - Confirm hold results in ugly error

Bug 16942 - Confirm hold results in ugly error

Confirming a hold to set it to waiting will result in an DBIC error in
master.

Test Plan:
1) Attempt to check in an item on hold and confirm the hold
2) Note the error
3) Apply this patch
4) Repeat step 1
5) Note there is no error!

Signed-off-by: Mirko Tietgen <mirko@abunchofthings.net>
https://bugs.koha-community.org/show_bug.cgi?id=14942

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jesse Maseto <jesse@bywatersolutions.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>