And move some code to make control flow more obvious.
No functional change.

Change-Id: Iefaa96f664070ab2accade1857e1946e56df6902
Reviewed-on: https://go-review.googlesource.com/34285
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>