Bug 37483: Use cud-list for extend due dates tool

This patch switch the check in the script to 'cud-list' - we use the same form
submission if listing for preview or directly updating dates, so this may or may
not be a cud- action - assuming it is restores script functionality.

See bug 37941 for updating forms to not share actions

To test:
1 - Checkout some items to patrons of at least two libraries
2 - Tools -> Batch extend due dates
3 - Select nothing except 'preview' and submit
4 - Blank screen
5 - Apply patch, repeat
6 - It works!
7 - Filter by library and confirm it still works
8 - Sign off!

Signed-off-by: Janusz Kaczmarek <januszop@gmail.com>

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>

tools/batch_extend_due_dates.pl

@@ -46,7 +46,7 @@ my @issue_ids;
 if ( $op eq 'form' ) {
     $template->param( view => 'form', );
 }
-elsif ( $op eq 'list' ) {
+elsif ( $op eq 'cud-list' ) {
 
     my @categorycodes     = $input->multi_param('categorycodes');
     my @itemtypecodes     = $input->multi_param('itemtypecodes');