Steps to Reproduce

<zk>
    <button label="click me" onClick="" />
</zk>

1. Browse any ZUL page, then stop the server.
2. Click something that sends the data to the server.
3. In a confirmation dialog, choose yes to resend.

Current Result

Uncaught (in promise) ReferenceError: ajaxReqResend is not defined
    ajaxSendNow 
    promise callback*ajaxSendNow
    sendNow 
    ajaxSend2 

Expected Result

No JS error

Debug Information

In ZK-3709 / ZK-550, the method ajaxReqResend was moved to zAu object.
https://github.com/zkoss/zk/blob/69ce6763661b1c94b183978c1a277bc93fd4d206/zk/src/archive/web/js/zk/au.js#L290
https://github.com/zkoss/zk/blob/69ce6763661b1c94b183978c1a277bc93fd4d206/zk/src/archive/web/js/zk/au.js#L1056

Workaround