message: Fix end of mission crash with mission server
diff: @@ -336,7 +336,10 @@ void MissionRawServerImpl::set_current_seq(std::size_t seq)
  _current_seq = seq;
  - auto converted_item = convert_item(_current_mission.at(_current_seq));
  + // If mission is over, just set item to last one again
  + auto item = seq == _current_mission.size() ? _current_mission.back() :
  + _current_mission.at(_current_seq);
  + auto converted_item = convert_item(item);
  _parent->call_user_callback([this, converted_item]() {
  if (_current_item_changed_callback) {
  _current_item_changed_callback(converted_item);
  