Bug 9809: [QA Follow-up] Remove warnings from Hold.pm

Bug 9809: [QA Follow-up] Remove warnings from Hold.pm

Resolves two warnings on a uninitialized found column:
holds: Use of uninitialized value in string eq at /home/koha/testclone/Koha/Hold.pm line 53., referer: http://test.rijkskoha.nl:28080/cgi-bin/koha/circ/circulation.pl?borrowernumber=152
holds: Use of uninitialized value in string eq at /home/koha/testclone/Koha/Hold.pm line 74., referer: http://test.rijkskoha.nl:28080/cgi-bin/koha/circ/circulation.pl?borrowernumber=152

Test plan:
Run t/db_dependent/Hold.t.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>