Bug 21596: (follow-up) Handle updated_on part 2

Bug 21596: (follow-up) Handle updated_on part 2

It seems that I have over complicated things here, now
t/db_dependent/Koha/Object.t is failing

Apparently everything is ok with this change.
Test plan:
prove -r prove -r t/db_dependent/Koha/Object.t t/Auth_with_shibboleth.t
t/db_dependent/Patrons.t t/db_dependent/Koha/Patron*

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>