more: avoid double free() on exit

more: avoid double free() on exit

On 'q' command more(1) calls end_it() function with _exit(). The
_exit() may suspend program execution due to pending I/O on very
loaded server. In this time SIGINT may be delivered due to impatient
user who will press ^C.

And then end_it() cleanup function may be executed by signal handler
too. The result is double free()...

Addresses: https://bugzilla.redhat.com/show_bug.cgi?id=1403971
Signed-off-by: Karel Zak <kzak@redhat.com>