Fix for <rdar://problem/5524216> CrashTracer: [USER] 496 crashes in Safari at com.apple.WebCore: WebCore::Frame::eventHandler const + 6

        The CrashTracer shows a variety of crashes in different methods (including keyDown and keyUp). This change adds nil checks for the frame in 
        WebHTMLView to prevent future problems in other methods as well.

        * WebView/WebHTMLView.mm:
        (-[WebHTMLView validateUserInterfaceItemWithoutDelegate:]):
        (-[WebHTMLView keyDown:]):
        (-[WebHTMLView keyUp:]):
        (-[WebHTMLView flagsChanged:]):
        (-[WebHTMLView _selectionStartFontAttributesAsRTF]):
        (-[WebHTMLView _changeCSSColorUsingSelector:inRange:]):
        (-[WebHTMLView checkSpelling:]):
        (-[WebHTMLView showGuessPanel:]):
        (-[WebHTMLView indent:]):
        (-[WebHTMLView outdent:]):
        (-[WebHTMLView paste:]):
        (-[WebHTMLView _lookUpInDictionaryFromMenu:]):
        (-[WebHTMLView insertText:]):
        (-[WebHTMLView selectionTextRects]):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@28117 268f45cc-cd09-0410-ab3c-d52691b4dbfc