cmd/go: align checks of module path during initialization.
Fixes #45025.
Change-Id: I70c2b745f764484e4b3a2824adc470f168fb2c50
Reviewed-on: https://go-review.googlesource.com/c/go/+/320310
Trust: Jay Conrod <jayconrod@google.com>
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Jay Conrod <jayconrod@google.com> Reviewed-by: Bryan C. Mills <bcmills@google.com> Reviewed-by: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org>