message: core: fix uninitialized command
diff: @@ -512,7 +512,7 @@ bool SystemImpl::send_message(mavlink_message_t& message)
  void SystemImpl::send_autopilot_version_request()
  {
  // We don't care about an answer, we mostly care about receiving AUTOPILOT_VERSION.
  - MavlinkCommandSender::CommandLong command;
  + MavlinkCommandSender::CommandLong command{};
  command.command = MAV_CMD_REQUEST_AUTOPILOT_CAPABILITIES;
  command.params.maybe_param1 = 1.0f;
  