LibGL: Implement glDrawBuffer

Author: https://github.com/sunverwerth
Commit: 7cbaaf8366
Pull-request: https://github.com/SerenityOS/serenity/pull/9713
Reviewed-by: https://github.com/Quaker762 ✅

Userland/Libraries/LibGL/SoftwareRasterizer.cpp

@@ -334,7 +334,7 @@ static void rasterize_triangle(const RasterizerOptions& options, Gfx::Bitmap& re
             }
 
             // We will not update the color buffer at all
-            if (!options.color_mask)
+            if (!options.color_mask || options.draw_buffer == GL_NONE)
                 continue;
 
             // Draw the pixels according to the previously generated mask