Avoid exception on IE when browser window refocused after switching to another application.   Thanks DaveHS, fixes #16437 !strict.

git-svn-id: http://svn.dojotoolkit.org/src/dijit/trunk@30137 560b804f-0ae3-0310-86f3-f6aa0a117693
(cherry picked from commit 63251cef036907179f528838f131ad1badfdab01)