Bug 13456: Serials/Claims.t expects no subscriptions

Bug 13456: Serials/Claims.t expects no subscriptions

However, this is an unreasonable assumption for a system which
is in use (either lots of testing or production).

TEST PLAN
---------
1) Have a supplier with a late subscription.
2) prove t/db_dependent/Serials/Claims.t
   -- will fail
3) apply patch
4) prove t/db_dependent/Serials/Claims.t
   -- success
5) run koha qa test tools

Signed-off-by: Paola Rossi <paola.rossi@cineca.it>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>