Bugfix: Set prev ball positions to off before drawing new ones

[musabkilic]

Hi!

I noticed this bug when I was watching the livestream. Imagine there are two balls, just for the fun of it I'm going to call them Alice and Bob.

Time 1: Alice is at 3, 3 and has a velocity of 1, 1 LED 3,3 turned off LED 3,3 turned on Bob is at 4, 4 and has a velocity of 1, 1 LED 4,4 turned off LED 4,4 turned on

LEDs at 3,3 and 4,4 are on

Time 2: Alice is at 4, 4 and has a velocity of ...(irrelevant) LED 3,3 turned off (prev pos) LED 4,4 turned on Bob is at 5, 5 and has a velocity of ...(irr.) LED 4,4 turned off (prev pos) LED 5,5 turned on

Only the LED at 5,5 is on

The problem is that if there is a ball(Alice) following another ball(Bob) and its index is smaller than the other one(i.e. processed before Bob), the ball in the front(Bob) turns off the one in the back(Alice).

This is a small and quick fix, and there might be a better way to this.

Cheers!