[BUG] Creating Wall constraints seems to randomly fail

I created an example of physics with 4 walls and a sphere. I set the sphere in motion with `setVelocity` and setup the contraints with the walls. During motion of the sphere, I use a click event to setVelocity again. Randomly the wall constraints fail.

[Here is the example branch: https://github.com/talves/famous-engine-seed/tree/walls](https://github.com/talves/famous-engine-seed/tree/walls)

I may not be setting up the constraints correctly.