Fix null object reference error in use ability code
Wall collision fix

-Robot Enemies who are moving randomly no longer get stuck moving
towards walls. (they may still get stuck if the wall
transform.position.y is less than 0.5, since we needed to exclude low
collisions with the ground
-They will still get stuck if there's an obstacle between them and an
actual target.
Merge pull request #15 from jpmeenagh/Johns-7-AI-fixes

Johns 7 ai fixes