don't double free in lru_crawler on closed clients
don't double free in lru_crawler on closed clients

during finalization, a poll and deliberate close are run. if a client is
closed during the poll it might double free.

guikcd/memcached,guikcd/memcached,guikcd/memcached,elfchief/memcached,dormando/memcached,bpzhang/memcached,gencer/memcached,guikcd/memcached,elfchief/memcached,bpzhang/memcached,elfchief/memcached,gencer/memcached,memcached/memcached,gencer/memcached,bpzhang/memcached,dormando/memcached,memcached/memcached,dormando/memcached,dormando/memcached,elfchief/memcached,dormando/memcached,gencer/memcached,memcached/memcached,bpzhang/memcached,elfchief/memcached,guikcd/memcached,memcached/memcached,memcached/memcached,gencer/memcached