binlogsyncer.go connection was bad

we alter big table,use --throttle-flag-file to stop. next time we go on,but it report error.it had failed.

```
Copy: 402207953/690882057 58.2%; Applied: 3495134; Backlog: 1000/1000; Time: 23h59m30s(total), 23h59m30s(copy); streamer: mysql-bin.003922:1001886394; State: throttled, flag-file; ETA: 17h13m9s
2018/07/18 00:00:05 binlogsyncer.go:490: ESC[0;31m[error] connection was bad ESC[0m
2018/07/18 00:00:06 binlogsyncer.go:452: ESC[0;37m[info] begin to re-sync from (mysql-bin.003922, 1004281698)ESC[0m
2018/07/18 00:00:06 binlogsyncer.go:134: ESC[0;37m[info] register slave for master server 10.27.48.22:5002ESC[0m
2018/07/18 00:00:06 binlogsyncer.go:568: ESC[0;37m[info] rotate to (mysql-bin.003922, 1004281698)ESC[0
```
binlogsyncer.go cloud try again?we alter big big table,if failed,we only can restart....
version:gh-ost_v1.0.40