Natvis kills visualizer if a property has a generic

[DefaultRyan]

I was trying to use the natvis on a XAML UIElement. One of its properties returns an IVectorView of something or other.

Now, generics aren't supported, which isn't the end of the world, but in this case, the visualizer throws an exception that unwids the whole enumeration of the children properties, causing the visualizer pane to collapse and close.

This is unacceptably hostile, because devs can't control if system types have generics in them. We should be less hostile and simply put something like "not supported" on that property, and continue enumerating.