Someday we should write errchk in Go. But not today.

Fixes #20007

Change-Id: I61ccf3cfaa66a710782f8a2212a6a2b4040698da
Reviewed-on: https://go-review.googlesource.com/40950
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>