revlog-split: make sure the self._indexfile attribut is reset (issue6811) Before this change, after a transaction committing a file split, a revlog object would have its `self._indexfile` attribute desynchronised from the actual file storing the data. If that same object is reused (as we do for the manifest during clone bundles), this lead to the data being writting in the wrong location and the repository to go corrupt. We not properly reset the attribut when applicable and everything is back in working order.