Fix #125035: Stop widget_box from Drawing over Contents

The complaint shows the background of the box widget drawn over top of
its contents, the color picker. This is resolved by flushing the widget
cache so that other content draws after.

Pull Request: https://projects.blender.org/blender/blender/pulls/131525

source/blender/editors/interface/interface_widgets.cc

@@ -4386,6 +4386,11 @@ static void widget_box(uiBut *but,
   widgetbase_draw(&wtb, wcol);
 
   copy_v3_v3_uchar(wcol->inner, old_col);
+
+  /* Flush the cache so that we don't draw over contents. #125035 */
+  GPU_blend(GPU_BLEND_ALPHA);
+  UI_widgetbase_draw_cache_flush();
+  GPU_blend(GPU_BLEND_NONE);
 }
 
 static void widget_but(uiWidgetColors *wcol,