Dojo Toolkit: Issue on Floating Pane when closing and reopening it

In `closable` floatingPane, when I close the FloatingPane and try to reopen it, it throws error.

There seems to be issue in Dojo Framework itself cause I can face the same issue in Documentation sample itself.

For sample, you can refer to the page: [dojox.layout.FloatingPane](https://dojotoolkit.org/reference-guide/1.10/dojox/layout/FloatingPane.html)

in this sample follow below steps to reproduce the issue:

1. Click on Run button of Programmatic example
2. Click on Show me (It will show the floating pane)
3. On the top right corner, click on close button to close
4. Click on Show me button again. (This will not work)

Start by reproducing the failure in the dojox.layout.FloatingPane documentation sample using the listed close-and-reopen steps. Then inspect the FloatingPane implementation and determine why the Show me action no longer works after closing; done means the sample can close and reopen the pane without an error.

Written by the indexing model from the issue text.