Bug 7965: Silence warns in staff log

Bug 7965: Silence warns in staff log

Silence warns in C4::Bookseller::GetBooksellersWithLateOrders()

to test
1/ run prove t/db_dependent/Bookseller.t
   Notice lots of Use of uninitialized value $delay in numeric lt (<) at /var/lib/jenkins/jobs/Koha_master/workspace/C4/Bookseller.pm line 134 type lines
2/ apply patch
3/ run prove t/db_dependent/Bookseller.t
   Notice warns are gone

Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Tiny change, positive consequences.
Passes QA script and all tests.

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>