internal/frontend: fix unknown module path in ScheduleFetch

A bug is fixed that caused queue.ScheduleFetch to be called with unknown
module path when the request version was main or master.

Change-Id: I61894f4d45599a29ffb70450d7def8e87e93b4ba
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/308969
Trust: Julie Qiu <julie@golang.org>
Run-TryBot: Julie Qiu <julie@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
diff --git a/internal/frontend/unit.go b/internal/frontend/unit.go
index 438fb7c..61e88d9 100644
--- a/internal/frontend/unit.go
+++ b/internal/frontend/unit.go
@@ -145,9 +145,10 @@
 		go func() {
 			ctx, cancel := context.WithTimeout(context.Background(), 1*time.Minute)
 			defer cancel()
-			log.Infof(ctx, "serveUnitPage: Scheduling %q@%q to be fetched", info.modulePath, info.requestedVersion)
-			if _, err := s.queue.ScheduleFetch(ctx, info.modulePath, info.requestedVersion, "", false); err != nil {
-				log.Errorf(ctx, "serveUnitPage(%q): %v", r.URL.Path, err)
+			log.Infof(ctx, "serveUnitPage: Scheduling %q@%q to be fetched", um.ModulePath, info.requestedVersion)
+			if _, err := s.queue.ScheduleFetch(ctx, um.ModulePath, info.requestedVersion, "", false); err != nil {
+				log.Errorf(ctx, "serveUnitPage(%q): scheduling fetch for %q@%q: %v",
+					r.URL.Path, um.ModulePath, info.requestedVersion, err)
 			}
 		}()
 	}