Bug 18635: Koha::Patron->guarantees() should return results alphabetically

Bug 18635: Koha::Patron->guarantees() should return results alphabetically

To test:
1 - Add the same guarantor to a number of patrons, ensuring random order
alphabetically
2 - View the guarantors record, note unordered list of guarantees
3 - Apply patch
4 - Guarantees are alphabetical

Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
(cherry picked from commit fe6cb85c5580b582a0047769d88be23757df0ef5)
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>