/**
 * Procedure testing if a ship is in (one of) the specified track bits.
 * @param v Vehicle to examine.
 * @param data Pointer to TrackBits.
 * @return \a v if conditions are met, else \c NULL.
 */
static Vehicle *EnsureNoShipOnTrackProc(Vehicle *v, void *data)
{
	if (v->type != VEH_SHIP) return NULL;

	Ship *s = Ship::From(v);
	TrackBits tb = *(TrackBits *)data;
	if (s->state & tb) return v;

	return NULL;
}