Rx CompositeDisposable CopyTo bug

rxbug.cs

// View constructor
this.WhenActivated(() =>
{
    var disposable = new CompositeDisposable();
    
    // We never actually add an IDisposable to the CompositeDisposable for debugging reasons or whatever
    return disposable;
})

// This code will crash at https://github.com/reactiveui/ReactiveUI/blob/rxui6-master/ReactiveUI/Activation.cs#L89
// with an ArgumentOutOfRangeException because of a bug in the CopyTo method of CompositeDisposable, 
// where it doesn't accept an arrayIndex that has the same size as the array 
// (In this case, the array is empty and arrayIndex is zero)

// Special gimmick: This bug occurs only under Mono, as the List<IDisposable> in the constructor of CompositeDisposable
// uses the CopyTo method on an empty source, but the .NET version doesn't.

// Even easier to reproduce under Mono:
new List<IDisposable>(new CompositeDisposable());