dispatch: fix traceback when extension was tested with newer versions only The "worst" extension still is the one tested with the lowest tested version below the current version of Mercurial, but if an extension with was only tested with newer versions, it is considered a candidate for a bad extension, too. In this case extensions which have been tested with higher versions of Mercurial are considered better. This allows finding the oldest extension if ct can't be calculated correctly and therefore defaults to an empty tuple, and it involves less changes to the comparison logic during the current code freeze.