Memory leak fixed by reusing windows

I switched to SDL3 and still have memory leak issues repeatedly creating & destroying windows. Then I finally realized I could reuse the windows. After finishing it on the SDL3 version, I also updated this one to remove the leak. Now it won't leak at all, yeah.

However, WPF is still too bad at framerate, so the SDL3 version is still my focus. It should reach a similar progress by today, hopefully.