scrollview-scrollbars causes js error in IE7 when contentSize = widgetSize

Here is a special case. When we create a scrollView like this:

var SC = new Y.ScrollView({axis: 'y', render: true});

And, sometimes the content size is same as scrollView size......then,
this cause javascript error in IE7 . we traced the code found scrollview-scrollbars try
to setStyle top to 'NaNpx' . Later a suggested patch will be attached.