SDL_GetClipboardData can return stale data

[Susko3]

Repro steps (for Windows)

1. Store some data with SDL_SetClipboardData with mime type image/png (it doesn't reproduce with image/bmp)
2. In another application, copy some data. Could be a BMP image or some text.
   • calling SDL_SetClipboardText doesn't reproduce it
3. Call SDL_HasClipboardData with image/png → notice that it returns SDL_TRUE
4. Call SDL_GetClipboardData → notice that you get your original data back, even though logically, the clipboard should only have the other application's data

[Green-Sky]

This is more or less a duplicate of #8338 .
Nice to have more eyes on this :)

[Susko3]

Not really a duplicate, yours only involves externally setting the clipboard, while this one mixes internal and external.

[slouken]

Fixed!