Fixed a memory leak at window creation.

Windows updates the desktop display mode once at video init (in WIN_InitModes()) and once when creating a window (in WIN_RefreshDisplays())

Fixes https://github.com/libsdl-org/SDL/issues/7982
Fixes https://github.com/libsdl-org/SDL/issues/8189

(cherry picked from commit bea34c5380)

src/video/SDL_video.c

@@ -828,6 +828,9 @@ void SDL_SetCurrentDisplayMode(SDL_VideoDisplay *display, const SDL_DisplayMode
 
 void SDL_SetDesktopDisplayMode(SDL_VideoDisplay *display, const SDL_DisplayMode *mode)
 {
+    if (display->desktop_mode.driverdata) {
+        SDL_free(display->desktop_mode.driverdata);
+    }
     SDL_memcpy(&display->desktop_mode, mode, sizeof(*mode));
 }