bug fix

service/book/book.go

 			return nil, errors.New("借阅失败")
 		}
 		if book.LeftNum <= 0 {
-			utils.LogError("该图书已无库存: " + err.Error())
 			return nil, errors.New("该图书已无库存")
 		}
 		var borrowRecord = model.TaBookBorrowRecord{