Fix bug that would lose data near end of input pipe,

when poll() returns both POLLIN and POLLHUP.

os.c

@@ -184,7 +184,7 @@ iread(fd, buf, len)
  }
  }
  int fd_events = poll_events(fd, POLLIN|POLLHUP|POLLERR);
- if (fd_events & close_events)
+ if ((fd_events & close_events) && !(fd_events & POLLIN))
  {
  sigs |= S_INTERRUPT;
  reading = 0;