wayland: sanity check events at the source

Sanity check events before we throw them into
the event queue, as this makes it much easier
to track down the culprit.

gdk/wayland/gdkeventsource.c

@@ -151,6 +151,9 @@ _gdk_wayland_display_deliver_event (GdkDisplay *display,
 {
   GList *node;
 
+  if (!check_event_sanity (event))
+    g_warning ("Snap! delivering insane events\n");
+
   node = _gdk_event_queue_append (display, event);
   _gdk_windowing_got_event (display, node, event,
                             _gdk_display_get_next_serial (display));