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

tv42/old-go,tv42/old-go,gnanderson/go,gnanderson/go,pombredanne/go-deleteme,pombredanne/go-deleteme,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,pombredanne/go-deleteme,apparentlymart/golang,pombredanne/go-deleteme,gnanderson/go,gnanderson/go,pombredanne/go-deleteme,gnanderson/go,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,gnanderson/go,apparentlymart/golang,tv42/old-go,gnanderson/go,tv42/old-go,pombredanne/go-deleteme,apparentlymart/golang