Bug 24215: Correct display of guarantor relationship errors

Bug 24215: Correct display of guarantor relationship errors

Test plan:
1) Add some bad data to your borrower_relationships table. ( add or
   update a relationship such that the 'relationship' field contains a
   value not listed in the corresponding system preference.
2) Go to the about system information page and note the nasty display of
   ARRAY(whatever)
3) Apply the patch
4) Repeat step 2 and note that a list of bad values is now displayed
   instead.

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>