runtime: fix bug introduced in cl/10256043
runtime: fix bug introduced in cl/10256043

R=golang-dev, dave
CC=golang-dev
https://codereview.appspot.com/10260043

wesolows/golang-old,wesolows/golang,wesolows/golang,wesolows/golang,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang-old,wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang,firebitsbr/golang-old