NaNs completely deadlock draw.line

```py
import math
import pygame

pygame.init()

surf = pygame.Surface((500,500))

print("Starting")

pygame.draw.line(surf, "black", (0, 0), (math.nan, 100))

print("Done!")
```

This test script makes pygame-ce completely unresponsive, it can't even be CTRL-Ced.

I haven't looked into other draw functions.