message: mission: fix NAN casting to double
diff: @@ -1210,7 +1210,7 @@ Mission::Result MissionImpl::import_mission_items(Mission::mission_items_t &all_
  for (auto &p : json_mission_item["params"].array_items()) {
  if (p.is_null()) {
  // QGC sets params as `null` if they should be unchanged.
  - params.push_back(NAN);
  + params.push_back(double(NAN));
  } else {
  params.push_back(p.number_value());
  }
  