LibGfx: assert Bitmap::set_pixel does not write out of bounds

Author: https://github.com/peterdn
Commit: https://github.com/SerenityOS/serenity/commit/23c4f1a3d41
Pull-request: https://github.com/SerenityOS/serenity/pull/3899
Issue: https://github.com/SerenityOS/serenity/issues/3484
Reviewed-by: https://github.com/awesomekling

Libraries/LibGfx/Bitmap.h

@@ -300,11 +300,13 @@ inline Color Bitmap::get_pixel(int x, int y) const
 template<>
 inline void Bitmap::set_pixel<StorageFormat::RGB32>(int x, int y, Color color)
 {
+    ASSERT(rect().contains(x, y));
     scanline(y)[x] = color.value();
 }
 template<>
 inline void Bitmap::set_pixel<StorageFormat::RGBA32>(int x, int y, Color color)
 {
+    ASSERT(rect().contains(x, y));
     scanline(y)[x] = color.value(); // drop alpha
 }
 inline void Bitmap::set_pixel(int x, int y, Color color)