message: Add additional check for non-manadatory parameters
  The OnPutFile notification has non mandatory parameters
  `fileSize` and `length`. If the mobile application has no provided
  appropriate parameters SDL sends `fileSize`: null as json value to HMI.
  The commit fixes the issue and simply remove non mandatory parameter in
  case mobile app sends nothing for one.
diff: @@ -302,18 +302,16 @@ void PutFileRequest::SendOnPutFileNotification() {
  smart_objects::SmartObjectSPtr notification =
  std::make_shared<smart_objects::SmartObject>(
  smart_objects::SmartType_Map);
  -
  smart_objects::SmartObject& message = *notification;
  message[strings::params][strings::function_id] =
  hmi_apis::FunctionID::BasicCommunication_OnPutFile;
  -
  message[strings::params][strings::message_type] = MessageType::kNotification;
  message[strings::msg_params][strings::app_id] = connection_key();
  message[strings::msg_params][strings::sync_file_name] = sync_file_name_;
  message[strings::msg_params][strings::offset] = offset_;
  - if (0 == offset_) {
  - message[strings::msg_params][strings::file_size] =
  - (*message_)[strings::msg_params][strings::length];
  + if (0 == offset_ &&
  + !(*message_)[strings::msg_params].keyExists(strings::length)) {
  + message[strings::msg_params][strings::file_size] = length_;
  }
  message[strings::msg_params][strings::length] = length_;
  message[strings::msg_params][strings::persistent_file] = is_persistent_file_;
  