TEST PLAN:
1. Have multiple holds from multiple patrons and run the holds queue cron to populate the holds queue list.
2. Try sorting by patron and see that is sorts based on first name.
3. Apply patch
4. Try sorting again and now it should sort by surname.
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net> Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de> Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>