Don't minimize fullscreen windows when destroying them. Previously, we'd minimize fullscreen windows (if SDL_HINT_VIDEO_MINIMIZE_ON_FOCUS_LOSS was set) during SDL_DestroyWindow if they had keyboard focus, because we call SDL_SetKeyboardFocus(NULL) which yields a OnWindowsFocusLost event. Related to https://bugzilla.libsdl.org/show_bug.cgi?id=1840