When walking over unix sockets make sure the
queuer is present before accessing it.

https://jira.sw.ru/browse/PSBM-82796Reported-by: Vitaly Ostrosablin <vostrosablin@virtuozzo.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@virtuozzo.com>
Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.com>