Issue title: 显示“尚未建立连接”，可是看起来没有地方有报错
 Issue body: XX-Net Status:

sys-platform: AMD64, Windows-10-10.0.15063
os-system: Windows
os-version: 10.0.15063
os-release: 10
os-detail: Version:10-0; Build:15063; Platform:2; CSD:; ServicePack:0-0; Suite:256; ProductType:0
architecture: 32bit,WindowsPE
browser: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3163.91 Safari/537.36
xxnet-version: 3.6.15
python-version: 2.7.13
openssl-version: 16.0.0 TLSv1_2 h2:alpn

ipv6-status: 0
gws-ip-num: total:9266 good:6081
network-status: OK
connected-link: new:0 used:0
worker: h1:0 h2:0
scan-ip-thread-num: 0
ip-quality: 100
is-idle: 0
block-stat: OK
proxy_state: OK
ca_state: OK
Appid_Working: true
Appids_Out_Of_Quota: false
Appids_Not_Exist: false
Using_Public_Appid: false
 Comments: 
 Comment 0: 没有开启 ipv6，版本3.6.15，刚才可以用的。。。突然就断开了显示尚未建立连接
{'source': 'GithubIssues', 'repo_name_with_owner': 'XX-net/XX-Net', 'issue_id': 265498093, 'repo_stars': 36300.0}