Show error messages in UI if something goes wrong

cmd/frontend/sessions.go

@@ -99,8 +99,8 @@ func Login(c *b.Config, db *b.DB, s *b.CookieStore) http.HandlerFunc {
 		userName := r.PostFormValue("username")
 		password := r.PostFormValue("password")
 
-		id, ok := db.GetID(userName)
-		if !ok {
+		id := db.GetID(userName)
+		if id == 0 {
 			http.Error(w, fmt.Sprintf("no such user: %v", userName), http.StatusBadRequest)
 			return
 		}