[giow] (0) Make non-scripted <dialog> closing not throw uncaught exceptions.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=23478
Affected topics: CSS, HTML

git-svn-id: http://svn.whatwg.org/webapps@8344 340c8d12-0b0e-0410-8428-c7bf67bfef74