All of these are uints of different sizes, so checking >= 0 or < 0 are
effectively no-ops.

Found with staticcheck.

Change-Id: I16ac900eb7007bc8f9018b302136d42e483a4180
Reviewed-on: https://go-review.googlesource.com/56950Reviewed-by: Matt Layher <mdlayher@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Matt Layher <mdlayher@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>