Bug 8299 - overdue_notice.pl shows error messages

Bug 8299 - overdue_notice.pl shows error messages

fixes 2 warnings...

 Use of uninitialized value in pattern match (m//) at /usr/share/koha/bin/cronjobs/overdue_notices.pl line 659.
 Use of uninitialized value in pattern match (m//) at /usr/share/koha/bin/cronjobs/overdue_notices.pl line 670.

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>
Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>