message: examples: fix uninitialized data
  I found it when I ran the example with valgrind.
diff: @@ -684,7 +684,7 @@ bool sysid_compid_correct()
  bool request_gimbal_device_information(MavlinkPassthrough& mavlink_passthrough)
  {
  - MavlinkPassthrough::CommandLong command;
  + MavlinkPassthrough::CommandLong command{};
  command.command = MAV_CMD_REQUEST_MESSAGE;
  command.param1 = static_cast<float>(MAVLINK_MSG_ID_GIMBAL_DEVICE_INFORMATION);
  command.target_sysid = mavlink_passthrough.get_target_sysid();
  