Fix some undefined behaviour: signed overflow and over shift left.

Caught by UndefinedBehaviourSanitizer.

src/core/math_func.cpp

@@ -58,7 +58,7 @@ int GreatestCommonDivisor(int a, int b)
  */
 int DivideApprox(int a, int b)
 {
-	int random_like = ((a + b) * (a - b)) % b;
+	int random_like = (((int64) (a + b)) * ((int64) (a - b))) % b;
 
 	int remainder = a % b;
 

src/newgrf.cpp

@@ -8322,7 +8322,7 @@ static void CalculateRefitMasks()
 		}
 
 		/* Clear invalid cargoslots (from default vehicles or pre-NewCargo GRFs) */
-		if (!HasBit(_cargo_mask, ei->cargo_type)) ei->cargo_type = CT_INVALID;
+		if (ei->cargo_type != CT_INVALID && !HasBit(_cargo_mask, ei->cargo_type)) ei->cargo_type = CT_INVALID;
 
 		/* Ensure that the vehicle is either not refittable, or that the default cargo is one of the refittable cargoes.
 		 * Note: Vehicles refittable to no cargo are handle differently to vehicle refittable to a single cargo. The latter might have subtypes. */

src/track_func.h

@@ -61,7 +61,7 @@ static inline bool IsValidTrackdirForRoadVehicle(Trackdir trackdir)
  */
 static inline bool IsValidTrackdir(Trackdir trackdir)
 {
-	return (1 << trackdir & TRACKDIR_BIT_MASK) != 0;
+	return trackdir < TRACKDIR_END && ((1 << trackdir & TRACKDIR_BIT_MASK) != 0);
 }
 
 /**