GetTileDistance, GetEdgeDistance, GetCornerDistance not initialized for HexMap

[AurelWu]

as title states, they should be initialized in constructor but that has been forgotten.

[mrshanepaul]

For those that want to fix this, add this to the constructor of HexMap:

            GetTileDistance = new MapDistanceCalculatorTile(coordinateWrapper);
            GetEdgeDistance = new MapDistanceCalculatorEdges(coordinateWrapper);
            GetCornerDistance = new MapDistanceCalculatorCorners(coordinateWrapper);