wayland: Print an error when the display connection is closed by the server

Otherwise, it isn't immediately clear to the client application as to why its windows suddenly disappeared, and it received a quit event out of nowhere.

src/video/wayland/SDL_waylandevents.c

@@ -498,6 +498,7 @@ void Wayland_PumpEvents(SDL_VideoDevice *_this)
          */
         if (!Wayland_VideoReconnect(_this)) {
             d->display_disconnected = 1;
+            SDL_LogError(SDL_LOG_CATEGORY_VIDEO, "Wayland display connection closed by server (fatal)");
 
             /* Only send a single quit message, as application shutdown might call
              * SDL_PumpEvents