Removed unnecessary assert in WIN_SetWindowOpacity()

Fixes https://github.com/libsdl-org/SDL/issues/15896

(cherry picked from commit f0e99e7c7f9aa90d5ce2e3b8a69f72c23faf257e)

src/video/windows/SDL_windowswindow.c

@@ -1648,8 +1648,6 @@ bool WIN_SetWindowOpacity(SDL_VideoDevice *_this, SDL_Window *window, float opac
     HWND hwnd = data->hwnd;
     const LONG style = GetWindowLong(hwnd, GWL_EXSTYLE);
 
-    SDL_assert(style != 0);
-
     if (opacity == 1.0f) {
         // want it fully opaque, just mark it unlayered if necessary.
         if (style & WS_EX_LAYERED) {