Tigthen assertions

Motivated by #40

src/fellow_cache.c

@@ -1131,8 +1131,12 @@ fellow_cache_lru_chgbatch_apply(struct fellow_lru_chgbatch *lcb)
 
 	//DBG("%u/%u", lcb->n, !VTAILQ_EMPTY(&lcb->add));
 
-	if (lcb->n_rem == 0 && VTAILQ_EMPTY(&lcb->add))
+	if (lcb->n_rem == 0 && (VTAILQ_EMPTY(&lcb->add) || lcb->n_add == 0)) {
+		AZ(lcb->n_rem);
+		AZ(lcb->n_add);
+		assert(VTAILQ_EMPTY(&lcb->add));
 		return;
+	}
 
 	fco = lcb->fco;
 	CHECK_OBJ_NOTNULL(fco, FELLOW_CACHE_OBJ_MAGIC);
@@ -1142,15 +1146,22 @@ fellow_cache_lru_chgbatch_apply(struct fellow_lru_chgbatch *lcb)
 	n = lcb->n_rem;
 	while (n--) {
 		fcs = lcb->fcs[n];
+		CHECK_OBJ_NOTNULL(fcs, FELLOW_CACHE_SEG_MAGIC);
+		assert(fcs->fco == fco);
 		AZ(fcs->lcb_add);
 		AN(fcs->lcb_remove);
 		fcs->lcb_remove = 0;
 	}
+	n = 0;
 	VTAILQ_FOREACH(fcs, &lcb->add, lru_list) {
+		CHECK_OBJ_NOTNULL(fcs, FELLOW_CACHE_SEG_MAGIC);
+		assert(fcs->fco == fco);
 		AZ(fcs->lcb_remove);
 		AN(fcs->lcb_add);
 		fcs->lcb_add = 0;
+		n++;
 	}
+	assert(n == lcb->n_add);
 
 	AZ(pthread_mutex_lock(&lru->lru_mtx));
 	lru->n += lcb->n_add;
@@ -1165,6 +1176,7 @@ fellow_cache_lru_chgbatch_apply(struct fellow_lru_chgbatch *lcb)
 	VTAILQ_CONCAT(&lru->lru_head, &lcb->add, lru_list);
 	AZ(pthread_mutex_unlock(&lru->lru_mtx));
 	lcb->n_add = 0;
+	assert(VTAILQ_EMPTY(&lcb->add));
 	AZ(lcb->n_rem);
 }