Error when underlaying dialog is closed after the new one is open

[john357smith]

Follow this case:

1. open first dialog (from link or button)
2. open second dialog (from button from previous dialog) and close first dialog via 'close' command
3. close second dialog (via closing button)
4. try open first dialog again and stack trace will occur saying "Uncaught TypeError: Cannot read property '_focusTabbable' of undefined"

Workaround: close first dialog first then open a new one.

Tested on: latest Chrome and Firefox

Code example:

<script>
$(function() { 

   $("#link_test1").on('click', function() {
     $("#test_dlg1").dialog('open');
   });

   $("#test_dlg2").dialog({
      autoOpen: false,
      modal: true
   });

   $("#test_dlg1").dialog({
      autoOpen: false,
      modal: true,
      buttons: [
    		{
          text: "open",
 	  click: function() {
            $('#test_dlg2').dialog("open");
            $(this).dialog("close");
    			}
    		}
        ]
   });

});
</script>

<a href="#" id="link_test1">open</a>

<div id="test_dlg1" title="test1">
test1
</div>

<div id="test_dlg2" title="test2">
test2
</div>

[Scott González]

​https://github.com/jquery/jquery-ui/pull/1817

[Scott González]

In 5708046:

Dialog: Fix shared event handler for modal dialogs

The old logic worked when all widgets of the same type used the same
event namespace. However, now that each instance has its own namespace,
we cannot use _on() for shared event handlers.

Fixes #15182
Closes gh-1817

[Scott González]

#15198 is a duplicate of this ticket.