message: camera_server: ignore duplicate commands
  In case our ack hadn't arrived or arrived in time, it makes sense,
  that we get the command again.
diff: @@ -654,8 +654,9 @@ CameraServerImpl::process_image_start_capture(const MavlinkCommandReceiver::Comm
  if (total_images == 1) {
  if (seq_number <= _image_capture_count) {
  LogDebug() << "received duplicate single image capture request";
  + // We know we already captured this request, so we can just ack it.
  return _server_component_impl->make_command_ack_message(
  - command, MAV_RESULT::MAV_RESULT_DENIED);
  + command, MAV_RESULT::MAV_RESULT_ACCEPTED);
  }
  // MAV_RESULT_ACCEPTED must be sent before CAMERA_IMAGE_CAPTURED
  