In the process of NBD equipment pressurization, executing QEMU NBD will
lead to the failure of IO distribution and go to NBD_ Out process of trip().
If two or more IO go to the out process, client NBD will release in nbd_request_put().
The user after free problem that is read again in close().
Through the NBD_ Save the value of client > closing before the out process in trip
to solve the use after free problem.
Signed-off-by: wangjian161 <wangjian161@huawei.com>
