Bug 24214: Fix due date formatting when sticky

Bug 24214: Fix due date formatting when sticky

When checking out and sticky due date is selected, on the next screen
the due date is displayed iso-formatted, instead of following the
dateformat syspref

Test plan:
0/ Do not apply the patch
1/ Check an item out, with a selected due date. Tick "Remember for
session"
2/ Next screen you see the date like YYYY-MM-DD HH:MM
regarless the value of the dateformat syspref
3/ Apply this patch
4/ Reload the page
=> The date is correctly formatted
5/ Check an item out
=> Due date is correctly set

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>