Crash during scroll when latched
https://bugs.webkit.org/show_bug.cgi?id=133064

Reviewed by Simon Fraser.

* page/mac/EventHandlerMac.mm:
(WebCore::EventHandler::platformPrepareForWheelEvents): Prevent dereference of NULL
wheelEventTarget argument.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@169037 268f45cc-cd09-0410-ab3c-d52691b4dbfc