Bug 43192: Cast escape_str(obj) arg to string to use escapeHtml func

The escape_str function in the OPAC requires the argument to be a string,
and will throw a fatal error if passed a Number. This is because
String.prototype.escapeHtml is created by Koha and is not a JS standard.
This patch converts the object to a string before applying escapeHtml.

To test, apply the patch and log in to the OPAC.

- If necessary, add a list.
- Search for records in the catalog and add one or more of the results
  to your new list.
- Go to Lists -> Your lists.
- In the list of your lists, click the "Delete" link for the list you
  added records to.
  - You should see a confirmation modal, "Are you sure you want to
   delete this list?" showing the name of the list and the number of
   items on it.
  - Clicking "Yes, delete" should delete the list.

Sponsored-by: Athens County Public Libraries
Signed-off-by: Roman Dolny <roman.dolny@jezuici.pl>
Signed-off-by: David Cook <dcook@prosentient.com.au>
Signed-off-by: Pedro Amorim <pedro.amorim@openfifth.co.uk>

koha-tmpl/opac-tmpl/bootstrap/js/global.js

@@ -50,7 +50,7 @@ String.prototype.escapeHtml = function () {
     });
 };
 function escape_str(s) {
-    return s != null ? s.escapeHtml() : "";
+    return s != null ? s.toString().escapeHtml() : "";
 }
 
 function confirmDelete(message) {