hg: make _local() behave consistently on Python 3.8 (issue6287) Python 3.8 makes os.path.isfile quietly eat "path invalid" errors and return False instead of allowing the exception to propagate. Given that this is a change from 2018 (sigh) and it's mentioned in the release notes (double sigh) we're definitely too late to complain to Python about the behavior change, so open-code part of os.path.isfile() in this method so we can catch invalid-path errors and handle them appropriately. I confirmed that posixpath and ntpath both delegate to genericpath, which uses os.stat() under the covers. Differential Revision: https://phab.mercurial-scm.org/D8302