message: core: fix steps on server component init
  Instead of creating it in the desctructor, we create it right before
  sending out the first heartbeat.
diff: @@ -34,8 +34,6 @@ MavsdkImpl::MavsdkImpl() : timeout_handler(_time), call_every_handler(_time)
  }
  }
  - _default_server_component = server_component_by_id(_configuration.get_component_id());
  -
  _work_thread = new std::thread(&MavsdkImpl::work_thread, this);
  _process_user_callbacks_thread =
  @@ -508,6 +506,11 @@ void MavsdkImpl::add_connection(const std::shared_ptr<Connection>& new_connectio
  void MavsdkImpl::set_configuration(Mavsdk::Configuration new_configuration)
  {
  + // We just point the default to the newly created component. This means
  + // that the previous default component will be deleted if it is not
  + // used/referenced anywhere.
  + _default_server_component = server_component_by_id(new_configuration.get_component_id());
  +
  if (new_configuration.get_always_send_heartbeats() &&
  !_configuration.get_always_send_heartbeats()) {
  start_sending_heartbeats();
  @@ -517,11 +520,6 @@ void MavsdkImpl::set_configuration(Mavsdk::Configuration new_configuration)
  stop_sending_heartbeats();
  }
  - // We just point the default to the newly created component. This means
  - // that the previous default component will be deleted if it is not
  - // used/referenced anywhere.
  - _default_server_component = server_component_by_id(new_configuration.get_component_id());
  -
  _configuration = new_configuration;
  }
  @@ -700,6 +698,12 @@ void MavsdkImpl::process_user_callbacks_thread()
  void MavsdkImpl::start_sending_heartbeats()
  {
  + // Before sending out first heartbeats we need to make sure we have a
  + // default server component.
  + if (_default_server_component == nullptr) {
  + _default_server_component = server_component_by_id(_configuration.get_component_id());
  + }
  +
  if (_heartbeat_send_cookie == nullptr) {
  call_every_handler.add(
  [this]() { send_heartbeat(); }, HEARTBEAT_SEND_INTERVAL_S, &_heartbeat_send_cookie);
  