Disable vehicle sounds entirely when running headlessly

src/newgrf_sound.cpp

@@ -186,6 +186,7 @@ SoundID GetNewGRFSoundID(const GRFFile *file, SoundID sound_id)
  */
 bool PlayVehicleSound(const Vehicle *v, VehicleSoundEvent event, bool force)
 {
+	if (IsHeadless()) return true;
 	if ((!_settings_client.sound.vehicle || _settings_client.music.effect_vol == 0) && !force) return true;
 
 	const GRFFile *file = v->GetGRF();