Bug 18858: Prevent warn when deleting a borrower debarment

Bug 18858: Prevent warn when deleting a borrower debarment

To test:
1) Look at intranet log
2) Go to delete a debarment on a borrower
3) Notice warn
4) Apply patch
5) Add a new debarment
6) Delete this debarment
7) Notice warn is gone

Sponsored-by: Catalyst IT
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 7ed66a6c8ae1c3c824e496c2d312e23db1dd8e41)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
(cherry picked from commit 7d2bd0482033ac106434aca59bab6b201a592fef)
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>