[ab] Bug in sdl:draw-pixel-* and sdl:read-pixel-*

[Michael Ben-Yosef]

Hi,

In the definitions of the above-mentioned lispbuilder-sdl functions, the 
macro sdl-base::check-bounds is used incorrectly, with (width surface) 
and (height surface) as the upper bounds, instead of (- (width surface) 
1) and (- (height surface) 1), respectively. This, of course, leads to 
possible memory corruption if one draws a pixel to the edge of the 
surface. The attached patch gives the required changes. Note that 
sdl:draw-line-* uses check-bounds correctly.

I haven't had any problems with sdl-gfx:draw-pixel-*. (Now I see that 
the SDL_gfx library does the range checking itself.) If one uses 
lispbuilder-sdl-gfx, should one use the sdl-gfx version of a symbol 
whenever it is exported by both the sdl and sdl-gfx packages?

Kind regards,

Michael
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