cmd/go/internal/modfetch/gitrepo: work around old git fetch hash behavior

For the git fetch --depth=1 attempt:

1. Use a ref instead of a hash if known.
2. Check for the older "no such remote ref" error in addition to the newer "unadvertised object" error.

Fixes golang/go#25102.

Change-Id: I38e66237c94c53989729bc0adf094980aaaf9093
Reviewed-on: https://go-review.googlesource.com/109518
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

vendor/cmd/go/internal/modfetch/gitrepo/fetch.go

diff --git a/vendor/cmd/go/internal/modfetch/gitrepo/fetch.go b/vendor/cmd/go/internal/modfetch/gitrepo/fetch.go
index 1e8345b..635f1a0 100644
--- a/vendor/cmd/go/internal/modfetch/gitrepo/fetch.go
+++ b/vendor/cmd/go/internal/modfetch/gitrepo/fetch.go
@@ -251,10 +251,14 @@
 
 	// Fetch it.
 	if len(hash) == 40 {
-		if _, err = codehost.Run(r.dir, "git", "fetch", "--depth=1", r.remote, hash); err == nil {
+		name := hash
+		if ref, ok := r.findRef(hash); ok {
+			name = ref
+		}
+		if _, err = codehost.Run(r.dir, "git", "fetch", "--depth=1", r.remote, name); err == nil {
 			goto Found
 		}
-		if !strings.Contains(err.Error(), "unadvertised object") {
+		if !strings.Contains(err.Error(), "unadvertised object") && !strings.Contains(err.Error(), "no such remote ref") {
 			return nil, nil, err
 		}
 	}