debug: Fix extra slash when urlprefix is empty.

Change-Id: Ibb2d480e83147ab52b237a3f0326efbde40d0d3e
diff --git a/services/debug/debug/browseserver/browseserver.go b/services/debug/debug/browseserver/browseserver.go
index 4f7505b..d770868 100644
--- a/services/debug/debug/browseserver/browseserver.go
+++ b/services/debug/debug/browseserver/browseserver.go
@@ -313,7 +313,11 @@
 				q.Set("s", children[0])
 				redirect.RawQuery = q.Encode()
 				ctx.Infof("Redirecting from %v to %v", r.URL, redirect)
-				http.Redirect(w, r, fmt.Sprintf("%s/%s", h.urlPrefix, redirect.String()), http.StatusTemporaryRedirect)
+				redirectString := redirect.String()
+				if h.urlPrefix != "" {
+					redirectString = fmt.Sprintf("%s/%s", h.urlPrefix, redirectString)
+				}
+				http.Redirect(w, r, redirectString, http.StatusTemporaryRedirect)
 				return
 			}
 		}