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>

admin/transport-cost-matrix.pl

@@ -42,7 +42,7 @@ my ($template, $loggedinuser, $cookie)
                             });
 my $use_transport_cost_matrix = C4::Context->preference("UseTransportCostMatrix");
 
-my $update = $input->param('op') eq 'set-cost-matrix';
+my $update = ( $input->param('op') // '' ) eq 'set-cost-matrix';
 
 my ($cost_matrix, $have_matrix);
 unless ($update) {