Fix trucks trying to drive into completed buildings instead of toward…

…s the building site.

More generally, check that the returned pathfinding result is for the correct
destination, rather than an old pathfinding job to a previous destination, leading
to the droid thinking it was going to the new destination when it really wasn't.

Droids were doing pathfinding, and occasionally they would pathfind to a building,
which happens to get completed in the same update, so next update they would try
to pathfind to the new building in the queue, but receive the path to the completed
building. They would then continue to drive into the old building, until arriving
at the new building (which never happens).

Probably fixes other issues with droids mysteriously going the wrong way.

Fixes ticket:3050 again (different bug, but similar symptom).

src/fpath.cpp

@@ -53,6 +53,7 @@ struct PATHRESULT
 	UDWORD		droidID;	///< Unique droid ID.
 	MOVE_CONTROL	sMove;		///< New movement values for the droid.
 	FPATH_RETVAL	retval;		///< Result value from path-finding.
+	Vector2i        originalDest;   ///< Used to check if the pathfinding job is to the right destination.
 };
 
 
@@ -96,6 +97,7 @@ static int fpathThreadFunc(void *)
 		result.droidID = job.droidID;
 		memset(&result.sMove, 0, sizeof(result.sMove));
 		result.retval = FPR_FAILED;
+		result.originalDest = Vector2i(job.destX, job.destY);
 
 		fpathExecute(&job, &result);
 
@@ -390,6 +392,7 @@ static FPATH_RETVAL fpathRoute(MOVE_CONTROL *psMove, int id, int startX, int sta
 			// Copy over select fields - preserve others
 			psMove->destination = psResult->sMove.destination;
 			psMove->numPoints = psResult->sMove.numPoints;
+			bool correctDestination = tX == psResult->originalDest.x && tY == psResult->originalDest.y;
 			psMove->pathIndex = 0;
 			psMove->Status = MOVENAVIGATE;
 			free(psMove->asPath);
@@ -406,6 +409,11 @@ static FPATH_RETVAL fpathRoute(MOVE_CONTROL *psMove, int id, int startX, int sta
 			objTrace(id, "Got a path to (%d, %d)! Length=%d Retval=%d", psMove->destination.x, psMove->destination.y, psMove->numPoints, (int)retval);
 			syncDebug("fpathRoute(..., %d, %d, %d, %d, %d, %d, %d, %d, %d) = %d, path[%d] = %08X->(%d, %d)", id, startX, startY, tX, tY, propulsionType, droidType, moveType, owner, retval, psMove->numPoints, ~crcSumVector2i(0, psMove->asPath, psMove->numPoints), psMove->destination.x, psMove->destination.y);
 
+			if (!correctDestination)
+			{
+				goto queuePathfinding;  // Seems we got the result of an old pathfinding job for this droid, so need to pathfind again.
+			}
+
 			return retval;
 		}
 
@@ -415,6 +423,7 @@ static FPATH_RETVAL fpathRoute(MOVE_CONTROL *psMove, int id, int startX, int sta
 		wzMutexUnlock(fpathMutex);
 		wzSemaphoreWait(waitingForResultSemaphore);  // keep waiting
 	}
+queuePathfinding:
 
 	// We were not waiting for a result, and found no trivial path, so create new job and start waiting
 	PATHJOB job;
@@ -473,15 +482,12 @@ FPATH_RETVAL fpathDroidRoute(DROID* psDroid, SDWORD tX, SDWORD tY, FPATH_MOVETYP
 	Position startPos = psDroid->pos;
 	Position endPos = Position(tX, tY, 0);
 	BASE_OBJECT *dstStructure = worldTile(endPos)->psObject;
-	if (psDroid->sMove.Status != MOVEWAITROUTE)
+	startPos = findNonblockingPosition(startPos, getPropulsionStats(psDroid)->propulsionType, psDroid->player, moveType);
+	if (dstStructure == NULL)  // If there's a structure over the destination, ignore it, otherwise pathfind from somewhere around the obstruction.
 	{
-		startPos = findNonblockingPosition(startPos, getPropulsionStats(psDroid)->propulsionType, psDroid->player, moveType);
-		if (dstStructure == NULL)  // If there's a structure over the destination, ignore it, otherwise pathfind from somewhere around the obstruction.
-		{
-			endPos   = findNonblockingPosition(endPos,   getPropulsionStats(psDroid)->propulsionType, psDroid->player, moveType);
-		}
-		objTrace(psDroid->id, "Want to go to (%d, %d) -> (%d, %d), going (%d, %d) -> (%d, %d)", map_coord(psDroid->pos.x), map_coord(psDroid->pos.y), map_coord(tX), map_coord(tY), map_coord(startPos.x), map_coord(startPos.y), map_coord(endPos.x), map_coord(endPos.y));
+		endPos   = findNonblockingPosition(endPos,   getPropulsionStats(psDroid)->propulsionType, psDroid->player, moveType);
 	}
+	objTrace(psDroid->id, "Want to go to (%d, %d) -> (%d, %d), going (%d, %d) -> (%d, %d)", map_coord(psDroid->pos.x), map_coord(psDroid->pos.y), map_coord(tX), map_coord(tY), map_coord(startPos.x), map_coord(startPos.y), map_coord(endPos.x), map_coord(endPos.y));
 	switch (psDroid->order.type)
 	{
 	case DORDER_BUILD: