elm_test: Fail nicely if plug can't connect

This makes sure that
  elementary_test -to "Window Plug"
exits nicely (with the exit policy on all window close) instead of
hanging forever with an invisible window.

@fix

src/bin/elementary/test_win_plug.c

@@ -194,6 +194,7 @@ test_win_plug(void *data, Evas_Object *obj EINA_UNUSED, void *event_info EINA_UN
    if (!elm_plug_connect(plug, "ello", 0, EINA_FALSE))
      {
         _notify_error(data, "Unable to connect to the Window Socket!");
+        evas_object_del(win);
         return;
      }