Fixed a crash bug when hlink_list is NULL and a link_u.links

pointer in one of the file_struct nodes is not.

hlink.c

@@ -135,7 +135,7 @@ void init_hard_links(struct file_list *flist)
 
 int hard_link_check(struct file_struct *file, int skip)
 {
-	if (!file->link_u.links)
+	if (!hlink_list || !file->link_u.links)
 		return 0;
 	if (skip && !(file->flags & FLAG_HLINK_EOL))
 		hlink_list[file->F_HLINDEX] = file->F_NEXT;