Fix a couple NPEs in Boat.cs

Assets/Scripts/Boat/Boat.cs

 
         private void FixedUpdate()
         {
+            if (WaypointGroup.Instance == null)
+                return;
             if (!RaceManager.RaceStarted)
             {
                 // race not started, make sure to keep boat fairly aligned.
 
         private void UpdateLaps()
         {
+            if (WaypointGroup.Instance == null)
+                return;
             LapPercentage = WaypointGroup.Instance.GetPercentageAroundTrack(transform.position);
             var lowPercentage = _lastCheckpoint?.normalizedDistance ?? 0f;
             var highPercentage = _nextCheckpoint?.normalizedDistance ?? 1f;