internal/coverage/encodemeta: simplify appending zero values
Appending zero values directly.
Change-Id: Icfb6e135b6aa16662dd67bdbf64ea0f63c612b2f
GitHub-Last-Rev:
57547b94087f216e943362e507b2339dd385f568
GitHub-Pull-Request: golang/go#65291
Reviewed-on: https://go-review.googlesource.com/c/go/+/558576
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>