Showcase app ajax validation check

[Greg Huber]

Was looking at some client side validation, with the showcase app. I use
firefox and it was not working, it just returned Network or server error!

https://struts.apache.org/docs/ajax-validation.html

The ajax call was returning 400, so falls back onto the error function and
just displays the network error message.

Not sure the best way to make this cross-browser complaint, other than
adding a check?
..
error: function(xhr, textStatus, errorThrown) {
            if (restoreFunction) {
                restoreFunction();
            }
            // show user an error message
            if(xhr.status == 400) {
              _handleValidationResult(_form,
jQuery.parseJSON(xhr.responseText))
            } else {
              _handleValidationResult(_form, {errors: ['Network or server
error!']})
            }
        }
..