Add missing check for NULL in DIOCCHANGERULE. This prevents a crash in certain rare cases.
Add missing check for NULL in DIOCCHANGERULE. This prevents a crash in
certain rare cases.

ok mcbride@ dhartmei@

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars