Fixed bug that caused some UIScrollView delegate method to not fire

Presumably for performance reasons `UIScrollView` has some flags that mark whether its delegate implements some of the UIScrollViewDelegate methods:

    ...
    unsigned int delegateScrollViewDidScroll : 1; 
    unsigned int delegateScrollViewDidZoom : 1; 
    unsigned int delegateContentSizeForZoomScale : 1; 

The `respondsToSelector:` check occurs when the delegate is set, and only **if the delegate is different** than the already stored. Since the code keeps setting the same delegate, the UIScrollView won't recheck the realDelegate for implementations. I fixed the issue by nilling out the delegate, as we as reordering the realDelegate setter, to make sure the UIScrollView queries the correct object.