!2084 af_unix: Fix null-ptr-deref in unix_stream_sendpage().

Merge Pull Request from: @ci-robot 
 
PR sync from: Liu Jian <liujian56@huawei.com>
https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/message/PFJHLONGQGRV7MO52W2QBFIPYEVJP2IK/ 
 
https://gitee.com/src-openeuler/kernel/issues/I7Z7C9 
 
Link:https://gitee.com/openeuler/kernel/pulls/2084

 

Reviewed-by: Yue Haibing <yuehaibing@huawei.com>
Reviewed-by: Liu YongQiang <liuyongqiang13@huawei.com>
Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>