The version "" denotes the main module, which has no version. The
mvs.Reqs interface documentation hints this is allowed, but it's not
obvious from the implementation in modload.mvsReqs.Max.
Also, replace a related TODO with a comment in mvs.Downgrade.
Fixes #39042
Change-Id: I11e10908c9b3d8c2283eaa5c04bd8e1b936851fd
Reviewed-on: https://go-review.googlesource.com/c/go/+/234003
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Bryan C. Mills <bcmills@google.com>