!4643 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/CSOO2WWFIYGIR5SY7YPOAWIKD4ZUGAGX/ 
 
https://gitee.com/src-openeuler/kernel/issues/I92HXK 
 
Link:https://gitee.com/openeuler/kernel/pulls/4643

 

Reviewed-by: Liu YongQiang <liuyongqiang13@huawei.com>
Reviewed-by: zhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>