Red-Black tree iterator increment

[MikeGWem]

The iterator increment method for a Red-Black Tree has an edge case that fails to change the node pointer. If the current node of the iterator is the root and there are no right hand children (and obviously no parent) then the node referenced by the iterator does not change. This means that iterations are effectively halted with the code potentially looping.

I hit the same thing when testing a version I had written and thought I would check the "master version" so to speak.