SetCursor doesn't work with TypedArgumentPack

When you have an argument pack (`e.GetArgumentPack()`) and want to move the cursor (`typedPack.Pack.SetCursor(1)`) you'll get the following exception:

```
Cannot unwrap a null object.
```

I expect the typed argument pack to move the cursor as well or at least have a `SetCuror` in the ITypedArgumentPack.