Zero distance crash

[DaddyTheRunner]

The solar system simulator (part 6) crashes if two planets happen to have zero distance between them. Here's the error message Python generates:

$ python simulator.py
Traceback (most recent call last):
  File "simulator.py", line 144, in <module>
    calculateMovement()
  File "simulator.py", line 66, in calculateMovement
    nDirection = (direction[0] / magnitude, direction[1] / magnitude) # Normalis
ed Vector pointing in the direction of the force
ZeroDivisionError: float division by zero

[seanmtracey]

Ah, these are always fun! I'll write some code in a little bit to check for a 0 before we try and divide anything.