A simple assertion to keep once #25 is fixed

src/fellow_cache.c

@@ -3186,6 +3186,7 @@ fellow_cache_lru_work(struct worker *wrk, struct fellow_cache_lru *lru)
 	AZ(pthread_mutex_lock(&lru->lru_mtx));
 	//lint -e{850} loop variable modified in body
 	VTAILQ_FOREACH_SAFE(fcs, &lru->lru_head, lru_list, fcss) {
+		assert(fcs != fcss);
 		BUG25_CHECK(fcs);
 		if (fcss)
 			BUG25_CHECK(fcss);