Fix off-by-one in repack index loop

A blunder of mine (Álvaro) in commit 28d534e2ae.

Author: Lakshmi N <lakshmin.jhs@gmail.com>
Reviewed-by: Xiaopeng Wang <wxp_728@163.com>
Reviewed-by: John Naylor <johncnaylorls@gmail.com>
Discussion: https://postgr.es/m/CA+3i_M9ytFufvD8Tm0rhpfxuC4XrpgQDBHxM7NJQYxv488JW7w@mail.gmail.com

src/backend/commands/repack.c

@@ -3017,7 +3017,7 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap,
 		{
 			int			pos = foreach_current_index(ind_old);
 
-			if (unlikely(list_length(ind_oids_new) < pos))
+			if (list_length(ind_oids_new) <= pos)
 				elog(ERROR, "list of new indexes too short");
 			ident_idx_new = list_nth_oid(ind_oids_new, pos);
 			break;