Corrected XPath iterator for ancestor-or-self axes for runaway behaviour

Corrected XPath iterator for ancestor-or-self axes for runaway behaviour

Adding a test case for ancestor-or-self along the lines of the existing one for ancestor showed runaway, memory-eating behaviour. In changing CollectResults to remove the livelock, it seemed simplest to remove the extra yield of the root from MoveNextCore. I was unable to ascertain a good reason for producing this element in this special way compared to the AncestorIterator.