cmd/go: break after terminal loop condition
After the first time needCostly is set to true, there is no need to
continue checking the remaining args.
Change-Id: I07171ce50d20e2a917117a0f84c442fe978cb274
GitHub-Last-Rev:
6d0c19341b7a85d507c3ec4967bab5f83b0fad8d
GitHub-Pull-Request: golang/go#41859
Reviewed-on: https://go-review.googlesource.com/c/go/+/260638
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Trust: Daniel Martí <mvdan@mvdan.cc>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Go Bot <gobot@golang.org>