Bug 21597: Incorrect date value: '0' for column 'onloan'

Bug 21597: Incorrect date value: '0' for column 'onloan'

Fix t/db_dependent/Holds/DisallowHoldIfItemsAvailable.t

items.onloan
  `onloan` date DEFAULT NULL,

DBIx::Class::Storage::DBI::_dbh_execute(): Incorrect date value: '0' for
column 'onloan' at row 1 at /home/vagrant/kohaclone/t/lib/TestBuilder.pm
line 288

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
(cherry picked from commit 489c636316209d4f4e7d8648cc5832347e792076)
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>