more: exit if POLLHUP or POLLERR on stdin is received

more: exit if POLLHUP or POLLERR on stdin is received

more command continues to run in case stdin have closed the file and it
takes 100% of CPU. This is because revents on stdin send
POLLIN | POLLHUP | POLLERR once stdin is closed. more receives it even
though it is not requested in events. This is common Linux behaviour to
never mask out POLLHUP or POLLERR. The loop in more_key_command() runs
infinitely because more_poll() returns 0 and read_command() reads 0
bytes.

Steps to reproduce:
1. Setup /etc/systemd/logind.conf with KillUserProcesses=no
2. Add config "Defaults use_pty" in /etc/sudoers
3. Start an ssh session to the machine
4. # sudo su -
5. # more <big enough file>
6. kill the parent ssh process, say close the tab

At this time "more" runs with 100% CPU utilization.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>