message: mission: make mission_data lock scope smaller
diff: @@ -139,16 +139,20 @@ void MissionImpl::process_mission_ack(const mavlink_message_t &message)
  // We got some response, so it wasn't a timeout and we can remove it.
  _parent->unregister_timeout_handler(_timeout_cookie);
  + Mission::result_callback_t result_callback;
  {
  std::lock_guard<std::recursive_mutex> lock(_mission_data.mutex);
  - Mission::result_callback_t result_callback;
  result_callback = _mission_data.result_callback;
  + }
  if (mission_ack.type == MAV_MISSION_ACCEPTED) {
  // Reset current and reached; we don't want to get confused
  // from earlier messages.
  + {
  + std::lock_guard<std::recursive_mutex> lock(_mission_data.mutex);
  _mission_data.last_current_mavlink_mission_item = -1;
  _mission_data.last_reached_mavlink_mission_item = -1;
  + }
  {
  std::lock_guard<std::mutex> lock(_activity.mutex);
  _activity.state = Activity::State::NONE;
  @@ -166,7 +170,6 @@ void MissionImpl::process_mission_ack(const mavlink_message_t &message)
  report_mission_result(result_callback, Mission::Result::ERROR);
  }
  }
  -}
  void MissionImpl::process_mission_current(const mavlink_message_t &message)
  {
  