Select Generative Design examples panicking on overflow

[sbauer322]

Here's a handful of Generative Design examples that fail to load / run for me due to addition or subtraction overflows.

Each example should have a note on how to reproduce and the line it occurs on.

Let me know if you need more information from the stacktraces. This is on the master commit b127d30

p_2_1_1_03.rs

Triggers when I press the '4' key and there are many diagonals on screen.

thread 'main' panicked at 'attempt to subtract with overflow', generative_design/shape/p_2_1_1_03.rs:95:23

p_2_1_3_05.rs

Triggers when moving the mouse around the far right side.

thread 'main' panicked at 'attempt to subtract with overflow', generative_design/shape/p_2_1_3_05.rs:92:32

p_2_2_1_02.rs

Triggers when loading

thread 'main' panicked at 'attempt to add with overflow', generative_design/shape/p_2_2_1_02.rs:92:9