avoid crash when showing bg tooltip if callback is reached unexpectedly

src/bin/empc.c

@@ -771,7 +771,7 @@ bg_update_signal(void)
 static Evas_Object *
 bg_tooltip_cb(void *data EINA_UNUSED, Evas_Object *obj EINA_UNUSED, Evas_Object *tooltip)
 {
-   if (bgchooser) return NULL;
+   if (bgchooser || (!empd_song_item)) return NULL;
    return tooltip_create(tooltip, empd_song_item);
 }