more: fix buffer overflow

The bug has been probably introduced by commit
1ac300932deab8dea2c43050921bbbdb36d62ff1.

Reported-by: "Dr. David Alan Gilbert" <dave@treblig.org>
References: https://bugzilla.novell.com/show_bug.cgi?id=829720
Signed-off-by: Karel Zak <kzak@redhat.com>