Bug 14153: Noisy warns in admin/transport-cost-matrix.pl

 Bug 14153: Noisy warns in admin/transport-cost-matrix.pl

To test:

1) Go to Admin -> Transport cost matrix
2) Notice the warns in the error log
3) Apply the patch and refresh page
4) Notice page still works but no warns in error log

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Amended patch: Init a $op variable, if it must be reused later.

Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>
(cherry picked from commit 825d68ee8696a2c3f3a2a95c0d148015f02a5ae9)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>