Reviewed by Beth.

    Reviewed by Beth.

        Another fix for 4098083 to apply to sliders.

        <rdar://problem/4098083> REGRESSION (125-312): crash
        in [KWQTableView resignFirstResponder] selecting from JS menu
        (car4you.at, etc.)

        Since it is possible that a render widget's eventFilterObject
        has been destroyed even though the render widget is still ref-ed,
        we need to nil-check the eventFilterObject before we use it to get
        the eventFilter.

        * kwq/KWQSlider.mm:
        (-[KWQSlider becomeFirstResponder]): Added nil check.
        (-[KWQSlider resignFirstResponder]): Added nil check.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@11386 268f45cc-cd09-0410-ab3c-d52691b4dbfc