Don't apply creation window flags to external windows.

Whoever provided the window has already set it up the way they want it.

Fixes SDL removing iconified or maximized state when creating a window from an existing OS window.

src/video/SDL_video.c

@@ -2146,9 +2146,14 @@ static void ApplyWindowFlags(SDL_Window *window, SDL_WindowFlags flags)
 static void SDL_FinishWindowCreation(SDL_Window *window, SDL_WindowFlags flags)
 {
  PrepareDragAndDropSupport(window);
- ApplyWindowFlags(window, flags);
- if (!(flags & SDL_WINDOW_HIDDEN)) {
- SDL_ShowWindow(window);
+
+ if (window->flags & SDL_WINDOW_EXTERNAL) {
+ // Whoever has created the window has already applied whatever flags are needed
+ } else {
+ ApplyWindowFlags(window, flags);
+ if (!(flags & SDL_WINDOW_HIDDEN)) {
+ SDL_ShowWindow(window);
+ }
  }
 }