nvda

63211573 - NVDAObjects.IAccessible.MSHTML.MSHTML's next, previous, firstChild and lastChild properties: properly handle the case where the HTMLNode we get is None -- just return None, rather than trying to instanciate an object with no HTMLNode. This may have previously worked in main as the NVDAObject instanciation would have returned None, but now this does not happen so we can not rely on that.