Test VTAILQ_CONCAT with empty first list

src/fellow_cache.c

@@ -5786,6 +5786,21 @@ t_cache(unsigned chksum)
 	}
 }
 
+static void
+t_tailq_concat(void)
+{
+	struct fellow_cache_seg	fcs[1];
+	struct fellow_cache_lru_head	h1[1], h2[2];
+
+	INIT_OBJ(fcs, FELLOW_CACHE_SEG_MAGIC);
+	VTAILQ_INIT(h1);
+	VTAILQ_INIT(h2);
+	VTAILQ_INSERT_TAIL(h2, fcs, lru_list);
+	VTAILQ_CONCAT(h1, h2, lru_list);
+	assert(VTAILQ_FIRST(h1) == fcs);
+	AZ(VTAILQ_NEXT(fcs, lru_list));
+}
+
 int
 main(int argc, char **argv)
 {
@@ -5794,6 +5809,8 @@ main(int argc, char **argv)
 	DBG("fellow_busy %zu", sizeof(struct fellow_busy));
 	assert(sizeof(struct fellow_busy) <= MIN_FELLOW_BLOCK);
 
+	t_tailq_concat();
+
 #ifdef HAVE_XXHASH_H
 	l = FH_LIM;
 #else