message: Fix usage of _uuid_initialized
  The UUID concerns an Autopilot system, so it should not affect
  set_connected() for other kinds of systems
diff: @@ -195,15 +195,14 @@ void SystemImpl::process_heartbeat(const mavlink_message_t& message)
  }
  }
  - // We do not call on_discovery here but wait with the notification until we know the UUID.
  -
  // If the component is an autopilot and we don't know its UUID, then try to find out.
  - if (is_autopilot(message.compid) && !have_uuid()) {
  + // If it's an autopilot, set_connected() will be called in process_autopilot_version().
  + if (is_autopilot(message.compid) && !_uuid_initialized) {
  request_autopilot_version();
  - }
  -
  + } else {
  set_connected();
  }
  +}
  void SystemImpl::process_autopilot_version(const mavlink_message_t& message)
  {
  @@ -508,7 +507,7 @@ void SystemImpl::set_connected()
  {
  std::lock_guard<std::mutex> lock(_connection_mutex);
  - if (!_connected && _uuid_initialized) {
  + if (!_connected) {
  LogDebug() << "Discovered " << _components.size() << " component(s) "
  << "(UUID: " << _uuid << ")";
  