Fix async dns lookup bug

_swAio_event->buf is not set zero in swoole_async_dns_lookup
fix async dns lookup bug
merge origin matser

merge origin matser
Merge pull request #1 from swoole/master

merge origin matser
Merge pull request #2 from swoole/master

thread safe
fix bug
Merge branch 'master' of github.com:sam198542/swoole
Merge branch 'master' of git://github.com/swoole/swoole-src into swoole-master
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Merge branch 'swoole-master'
Merge branch 'master' of git://github.com/swoole/swoole-src
Fix async dns lookup bug
Merge pull request #99 from sam198542/master

Fix async dns lookup bug