Windows: Added missing NULL check after SDL_stack_alloc().

SDL_stack_alloc() might wrap SDL_malloc() which can return NULL.

src/video/windows/SDL_windowsframebuffer.c

@@ -42,6 +42,9 @@ int WIN_CreateWindowFramebuffer(_THIS, SDL_Window * window, Uint32 * format, voi
     /* Find out the format of the screen */
     size = sizeof(BITMAPINFOHEADER) + 256 * sizeof (RGBQUAD);
     info = (LPBITMAPINFO)SDL_stack_alloc(Uint8, size);
+    if (!info) {
+        return SDL_OutOfMemory();
+    }
 
     SDL_memset(info, 0, size);
     info->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);