misc: provide url even in case of failure

(local change found on mandayejs.test, dated 2018-10-18)

mandayejs/do_login.js

@@ -96,6 +96,7 @@ page.open(input.address, function(status) {
             } else {
                 output['result'] = 'failure';
                 output['reason'] = 'authentication';
+                output['url'] = page.frameUrl;
             }
             mandaye_exit(JSON.stringify(output));
         }