Bug 25531: Debar patron if needed when checkin is backdated

Bug 25531: Debar patron if needed when checkin is backdated

If think this case does not apply to real-life, but the logic needs to
be fixed.
If an item is due now, and AddReturn is called now with a return date in
the future, the issue is overdue and the patron must be debarred.
However it is not as we compare with now and not the return date

Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>