graphics.c does not clip

[rasky]

graphics.c does not perform any clipping, which means that it's possible to make the application crash by writing outside the target surface.

Following the current libdragon approach, I think it would be useful to implement some clipping on the surface extents. This could be easily done within the __set_pixel macro at the expense of some performance, or better done function by function before entering the per-pixel loop.