Bug 23893: Catch dt_from_string exceptions

Bug 23893: Catch dt_from_string exceptions

This patch adds exception handling to the attributes_from_api() method.
This can happen with invalid date/datetimes, for example.

Tests are added:

1. Apply this patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/Koha/Object.t
=> SUCCESS: Tests pass!
3. Sign off :-D

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>