Cell sizes under 4px cause errors

[briansmiley]

Choosing pixel size 1 or 2 leads to an Array allocation error of some kind; size 3 oddly leads to a heap overflow.

[briansmiley]

Comes from int overflow in the Grid area value. Base screen area of 512x256 is 131,072, int ceiling is 32,767, so dividing dimensions by less than 4 doesn't let you store area in an int. Probably easily fixable, but alternatively it would be nice not to store each cell (just a bool, representable by 1 bit) as an entire register value taking up 16x needed space in heap.