Bug 43394: DT - Cast pageLength to Integer

In "Edit patron card batch" the pageLength is coming from the syspref,
the value is a string.
But DataTable's needs an integer.
Let's fix this in datatables.js, in the kohaTable's constructor

Test plan:
Got to cgi-bin/koha/patroncards/edit-batch.pl
Enter more than 20 borrowernumbers and "Add patron(s)"
Click "next" and notice that with this patch the pagination works.
Without this patch the JS error is
"Uncaught TypeError: can't access property "nTr", p is undefined"

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Pedro Amorim <pedro.amorim@openfifth.co.uk>

koha-tmpl/intranet-tmpl/prog/js/datatables.js

@@ -1585,6 +1585,13 @@ function update_search_description(
             }
         }
 
+        if (
+            settings.pageLength !== undefined &&
+            !Number.isInteger(settings.pageLength)
+        ) {
+            settings.pageLength = parseInt(settings.pageLength, 10);
+        }
+
         settings["buttons"] = _dt_buttons({ settings, table_settings });
 
         var default_column_defs = [