small memory leak in esp_mqtt_client_init error path (IDFGH-2235)

[AxelLin]

In IDF-4.0-beta2.
Need to free client->event.error_handle if create mutex for client->api_lock fails.

`
diff --git a/mqtt_client.c b/mqtt_client.c
index 19458f7dc7aa..2343a5c1c78c 100644
--- a/mqtt_client.c
+++ b/mqtt_client.c
@@ -374,6 +374,7 @@ esp_mqtt_client_handle_t esp_mqtt_client_init(const esp_mqtt_client_config_t *co
}
client->api_lock = xSemaphoreCreateMutex();
if (!client->api_lock) {

•    free(client->event.error_handle);
     free(client);
     return NULL;
  

  }

`

[ESP-Marius]

Thanks for reporting this issue, we'll make sure to fix this in our next MQTT update.