Bug 21597: Field 'amount' doesn't have a default value

Bug 21597: Field 'amount' doesn't have a default value

Fix t/db_dependent/Accounts.t

Default value could be 0, or left as it.
It seems that the different initialisation we have in the code pass a
value for 'amount'

account_offsets.amount
  `amount` decimal(26,6) NOT NULL,

DBIx::Class::Storage::DBI::_dbh_execute(): Field 'amount' doesn't
have a default value at /home/vagrant/kohaclone/Koha/Object.pm line 125

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>