Added error catching for ObstacleSpawner.cs
Added error catching for ObstacleSpawner.cs

There is currently an ArgumentOutOfRangeException in ObstacleSpawner.cs
which is happening because we don't have any objects in it to spawn this
isn't an issue once I figured it out. It doesn't throw errors now if the
array is out of bounds.

Darth-Knoppix/terrasurge