!4645 f2fs: explicitly null-terminate the xattr list

Merge Pull Request from: @ci-robot 
 
PR sync from: Zizhi Wo <wozizhi@huawei.com>
https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/message/77ZHV2BEGUJMUC2OHDP23INKSTPDTUZC/ 
 
https://gitee.com/src-openeuler/kernel/issues/I92HXK 
 
Link:https://gitee.com/openeuler/kernel/pulls/4645

 

Reviewed-by: zhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>