largefiles: ensure lfutil.getstandinmatcher() only matches standins Previously, simply having the largefiles extension loaded without any largefiles added would crash when amending with -I. The problem was with no files in the matcher, the pattern list of files joined with 'standindir' was empty, and scmutil.match() would match everything. In lfutil.composestandinmatcher(), the match function is used to test if the file is a standin, and after getting a false positive, proceeds to call lfutil.splitstandin(). This returns None because it isn't a standin, which blows up when passed to rmatcher.matchfn(). Manually overriding _always in getstandinmatcher() probably isn't necessary anymore, but we leave well enough alone on stable. This regressed in ab618e52788a.