Bug 29139: Fix incorrect relation call

Bug 29139: Fix incorrect relation call

The bug here was worse than originally thought. We were calling the
wrong relation too.. we should probably add some exceptions to catch
this, it confuses me every single time!

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>