more: make sure we have data on stderr

more: make sure we have data on stderr

more(1) uses more_poll() to monitor data on stdin, stderr, and
signals. It is used before read_command(), but this function only
reads from stderr. Therefore, if any other non-stderr event occurs,
this function will wait on read(). In this case, more(1) will not
react to signals anymore. We need to ensure that more(1) only waits in
more_poll().

Try

 for x in {1..1000}; do echo "line $x"; done | more

to reproduce.

Reported-by: Radka Skvarilova <rskvaril@redhat.com>
Signed-off-by: Karel Zak <kzak@redhat.com>
(cherry picked from commit 640b9480bd3efc0f4bc7f38a785d02cda70ec5c3)