Out of bounds access in paint_uniform_rectangle

[KasumiArai]

I put together the imgui demo containing ImGui::ShowDemoWindow() (the same imgui commit contained in third_party) with this software renderer, and had a consistent crash when opening Widgets, Color/Picker Widgets in the demo window. The Windows 10 window size was 889x528. The position and size of the demo window (as reported by imgui.ini):
[Window][ImGui Demo]
Pos=75,38
Size=691,3418
Collapsed=0

I believe I traced the issue to this line:

imgui_software_renderer/src/imgui_sw.cpp

Line 239 in e942aca

uint32_t last_target_pixel = target.pixels[min_y_i * target.width + min_x_i];

max_y_i and min_y_i were both 528. That would prevent the for loops from drawing a row, but the last_target_pixel line still accessed memory beforehand. To fix, I set last_target_pixel to 0, as was done here:

imgui_software_renderer/src/imgui_sw.cpp

Line 432 in e942aca

uint32_t last_target_pixel = 0;

Apologies if a pull request might have been preferred. I was not sure if I should do so unsolicited.

Thanks for putting this together, it has been a massive help for a certain project of mine

[emilk]

The problem is that paint_uniform_rectangle needs an early-out before indexing into target.pixels:

if (max_x_i <= min_x_i || max_y_i <= min_y_i) {
    return;
}