update user only if it exists

persistence.go

@@ -362,6 +362,14 @@ func updateUser(username, password string) {
 	conn := globalPool.Get()
 	defer conn.Close()
 	logit("updateUser: " + username)
+
+        // we exit if user does not exit
+	exists, _ := redis.Bool(conn.Do("EXISTS", userPrefix+username))
+	if !exists {
+	        logit("updateUser: User does not exist: " + username)
+		return
+	}
+
 	pwd := []byte(password)
 	hashedPassword, err := bcrypt.GenerateFromPassword(pwd, bcrypt.DefaultCost)
 	if err != nil {