Problem Description:

Tabbox doesn't select second tab when first tab is invisible at the beginning.
come from forum post: http://forum.zkoss.org/question/92244/second-tabpanel-is-not-loading-if-first-one-is-hidden/

Reproducing Steps:

1. run the zul below:

   <zk>
       <tabbox>
           <tabs>
               <tab id="first" label="First Panel" closable="false" visible="false"/>
               <tab id="second" label="Second Panel" closable="false" visible="true"/>
           </tabs>
           <tabpanels>
               <tabpanel visible="false">
                   First Panel
               </tabpanel>
               <tabpanel visible="true">
                   Second Panel
               </tabpanel>
           </tabpanels>
       </tabbox>
   </zk>
   

Expected:

second panel's content shows up.

Actual:

second panel's content doesn't shows up.