Add missing sanity check to tty operation.
Acked-by: NAlan Cox <alan@redhat.com>
Signed-off-by: NEugene Teo <eteo@redhat.com>
Cc: Jeff Garzik <jeff@garzik.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NJeff Garzik <jgarzik@redhat.com>