message: fix go mirror when no changes
diff: @@ -116,9 +116,9 @@ if __name__ == "__main__":
  cloneGoProtobufs(repo)
  last_sha = findLastSyncSHA(repo)
  changes = updatedSinceSHA(repo, last_sha)
  - new_sha = changes[0]
  if changes:
  print('Changes detected: %s' % changes)
  + new_sha = changes[0]
  syncGoProtobufs(output, repo)
  writeRevisionInfo(repo, new_sha)
  publishGoProtobufs(repo, new_sha)
  