Bug 27921: Log correct timestamp for HOLD MODIFY when set waiting

Bug 27921: Log correct timestamp for HOLD MODIFY when set waiting

The HOLD MODIFY log at the end of ModReserveAffect is not using an
up-to-date $hold object.

$hold is modified at
1201         $hold->set_waiting($desk_id);
But not refreshed before logged (and so the timestamp is not logged
correctly).

Test plan:
Turn on HoldsLog
Place an item on hold
Check it in to mark it waiting

Confirm that the timestamp logged is the one from the check in, not when
you created the hold

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>