fix bounds check in error recovery (thanks to avp@mit.edu)
fix bounds check in error recovery
(thanks to avp@mit.edu)

R=rsc
CC=golang-dev
http://codereview.appspot.com/1998041
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go