x/vgo: ignore blank lines in go.modverify

Fixes golang/go#24027.

Change-Id: I3d0d4768e5086ce176fc5d41211805fbd8bfc2e0
Reviewed-on: https://go-review.googlesource.com/104935
Reviewed-by: Russ Cox <rsc@golang.org>

vendor/cmd/go/internal/vgo/fetch.go

diff --git a/vendor/cmd/go/internal/vgo/fetch.go b/vendor/cmd/go/internal/vgo/fetch.go
index b76eb3d..30ad8f7 100644
--- a/vendor/cmd/go/internal/vgo/fetch.go
+++ b/vendor/cmd/go/internal/vgo/fetch.go
@@ -144,8 +144,12 @@
 			line, data = data[:i], data[i+1:]
 		}
 		f := strings.Fields(string(line))
+		if len(f) == 0 {
+			// blank line; skip it
+			continue
+		}
 		if len(f) != 3 {
-			base.Fatalf("vgo: malformed go.modverify:\n%s:%d: wrong number of fields", file, lineno)
+			base.Fatalf("vgo: malformed go.modverify:\n%s:%d: wrong number of fields %v", file, lineno, len(f))
 		}
 		mod := module.Version{Path: f[0], Version: f[1]}
 		modHash[mod] = append(modHash[mod], f[2])