examples/cxx: add missing header

examples/cxx/experimental/esp_mqtt_cxx/components/esp_mqtt_cxx/esp_mqtt_cxx.cpp

@@ -1,19 +1,12 @@
-// Copyright 2021 Espressif Systems (Shanghai) CO LTD
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//         http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
+/*
+ * SPDX-FileCopyrightText: 2021-2022 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
 
 #include <string>
 #include <algorithm>
+#include <stdexcept>
 
 #include "mqtt_client.h"
 #include "esp_log.h"