was referencing a nil WebView under validateUserInterfaceItem.
The validateUserInterfaceItem methods was being called at a time
when the WebHTMLView is being torndown.

<rdar://problem/5806229> A crash occurs at CallUIDelegateReturningBoolean()
while mousing down on menu bar after Xcode News window is opened

Reviewed by Ada Chan.

* WebView/WebHTMLView.mm:
(-[WebHTMLView validateUserInterfaceItem:]): NULL check the WebView and
return NO when it is nil. Adds a comment.
* WebView/WebPDFView.mm:
(-[WebPDFView validateUserInterfaceItem:]): Ditto.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@33415 268f45cc-cd09-0410-ab3c-d52691b4dbfc