FirmwareService not initialized

[shengxiang200788]

Hi Matth-x， Found firmwareService is not initialized in mocpp_initialize(), line 365:

    if (model.getFirmwareService() && credsJson && credsJson->containsKey("firmwareVersion")) {
        model.getFirmwareService()->setBuildNumber((*credsJson)["firmwareVersion"]);
    }

If change to 

    if (getFirmwareService() && credsJson && credsJson->containsKey("firmwareVersion")) {
        model.getFirmwareService()->setBuildNumber((*credsJson)["firmwareVersion"]);
    }

works fine.