tests: remove two misuses of nil pointers

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/12858044
spec: &x panics if x does

See golang.org/s/go12nil for the extended version.

R=golang-dev, r, adonovan
CC=golang-dev
https://codereview.appspot.com/12964043