Increases generic.rules coverage from 91% to 95%.

Change-Id: I981eb94f3cd10d2f87c836576a43786787a25d83
Reviewed-on: https://go-review.googlesource.com/23556
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Todd Neal <todd@tneal.org>