publish函数中，LOT是结构体，我创建了一个结构体指针new_n,并且用malloc赋予它地址空间，然后我用insert_tail_lot函数将new_n加入链表，并且用length_lot函数求出链表长度，并且赋给结构体中的issue.但是程序运行出现段错误，请问是哪里错了？

void publish(LOT *lot_head)
 {
         LOT *new_n = NULL;
             new_n = malloc(sizeof(LOT));

            insert_tail_lot(lot_head,new_n);
        new_n->issue = length_lot(lot_head);
        printf("第%d期\n",new_n->issue);
}

int insert_tail_lot(LOT *lot_head,LOT *new_n)
{
        if(new_n == NULL){
            return 1;
        }
        find_tail_lot(lot_head)->next = new_n;
        new_n->next = NULL;
   
            return 0;
}

LOT *find_tail_lot(LOT *lot_head)
{
        LOT *tail = NULL;
   
        tail = lot_head;
        while(tail->next != NULL)
            tail = tail->next;
            return tail;

}


int length_lot(LOT *lot_head)
{
        int len=0;
        LOT *cur=NULL;

        cur=lot_head->next;
        while(cur != NULL){
            len++;
            cur = cur->next;        
        }
        return len;
    }