Fix: pathfinders always tried to avoid docking tiles (even if nothing was on them) (#9522)

When coming across any docking tile (for example, all tiles around
an oilrig are docking tiles), it always at least added a penalty
of 3 times a normal tile, even when there are no ships on them.

In result, the pathfinder got suggested to always go around docking
tiles. This was most likely not the intention of the change made in
31db4f8d5e.

(cherry picked from commit f87fe395a7)

src/pathfinder/npf/npf.cpp

@@ -311,7 +311,7 @@ static int32 NPFWaterPathCost(AyStar *as, AyStarNode *current, OpenListNode *par
 
 	if (IsDockingTile(current->tile)) {
 		/* Check docking tile for occupancy */
-		uint count = 1;
+		uint count = 0;
 		HasVehicleOnPos(current->tile, VEH_SHIP, &count, &CountShipProc);
 		cost += count * 3 * _trackdir_length[trackdir];
 	}

src/pathfinder/yapf/yapf_ship.cpp

@@ -287,7 +287,7 @@ public:
 
 		if (IsDockingTile(n.GetTile())) {
 			/* Check docking tile for occupancy */
-			uint count = 1;
+			uint count = 0;
 			HasVehicleOnPos(n.GetTile(), VEH_SHIP, &count, &CountShipProc);
 			c += count * 3 * YAPF_TILE_LENGTH;
 		}