Bug 36196: Handling NULL data on ajax call

Bug 36196: Handling NULL data on ajax call

Test plan:

1) Update some data in your cities table, sample for one send:
"UPDATE cities SET city_state=NULL WHERE cityid=<id>"
2) Go on "/cgi-bin/koha/admin/cities.pl" and wait a entire life :)
3) Apply this patch
4) Rebuild your po files if needed
5) Reload the same page and now you get normally the datatable

Sponsored by: BibLibre
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
(cherry picked from commit e0856d0db648766ba1d65a4f784983a416ac4a35)
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>