message: add check if inotify_add_watch returns descriptor
diff: @@ -250,6 +250,11 @@ static void wait_hermit_available(void)
  else
  wd = inotify_add_watch(fd, "/sys/hermit", IN_MODIFY|IN_CREATE);
  + if (wd < 0) {
  + perror("inotify_add_watch");
  + exit(1);
  + }
  +
  while(1) {
  int length = read(fd, buffer, BUF_LEN);
  