Particle out of bounds fix

[sikora507]

I saw your comment in ofApp.cpp about bouncing off the edges which needs to be fixed.

I've written the app in GO and this fixes it:

Just don't check for < 0 and > max in single if.
If < 0, set position to 0, reverse velocity
If > max, set position to max, reverse velocity

[hunar4321]

Thanks a lot