do not fail if POLLHUP occurs while reading data
    
    This cause troubles when we send data to a pipe and close the
    file descriptor before data is read. The pipe is still readable,
    but POLLHUP is detected and we fail to read them.
    
    For example, this may cause a user beeing unable to log in.
    
    Now if POLLHUP appears, we read the pipe and then close it on
    the client side too.