A few staticcheck fixes (#539)

A few staticcheck fixes (#539)

This fixes a few small staticcheck issues; turns out that staticcheck
only compiles the files for the current GOOS:
https://staticcheck.io/docs/running-staticcheck/cli/build-tags/

You can run all systems with:

	staticcheck -matrix <<EOF
	windows: GOOS=windows
	linux: GOOS=linux
	freebsd: GOOS=freebsd
	openbsd: GOOS=openbsd
	netbsd: GOOS=netbsd
	darwin: GOOS=darwin
	illumos: GOOS=illumos
	EOF

The CI runner doesn't really support that, but it's little more than a
small wrapper around "go install" with some variables, so just use that
directly instead of the action.