crawler: remove bad mutex unlock during error
crawler: remove bad mutex unlock during error

Detail in: https://github.com/memcached/memcached/issues/741

memcached/memcached,dormando/memcached,dormando/memcached,memcached/memcached,dormando/memcached,dormando/memcached,memcached/memcached,memcached/memcached,dormando/memcached,memcached/memcached