Get the parent of non-SDL-created windows, for completeness

src/video/windows/SDL_windowswindow.c

@@ -366,7 +366,7 @@ WIN_CreateWindowFrom(_THIS, SDL_Window * window, const void *data)
         SDL_stack_free(title);
     }
 
-    if (SetupWindowData(_this, window, hwnd, NULL, SDL_FALSE) < 0) {
+    if (SetupWindowData(_this, window, hwnd, GetParent(hwnd), SDL_FALSE) < 0) {
         return -1;
     }