(svn r990) Fix a display bug in the order list:

TTD stores invalid orders different than OTTD, this resulted in empty lines in the order list. With the overhaul of the order system this got worse: no line was shown at all.
Fix this by sanity checking while loading and convert the orders accordingly.

vehicle.h

@@ -28,6 +28,9 @@ static inline Order UnpackOrder(uint16 packed)
 	return order;
 }
 
+Order UnpackOldOrder(uint16 packed);
+
+
 typedef struct VehicleRail {
 	uint16 last_speed;		// NOSAVE: only used in UI
 	uint16 crash_anim_pos;