filter: exited when invalid filter expression was given.
filter: exited when invalid filter expression was given.

Previously, lltsv continued processing after outputting such as the error message below
even if invalid filter expression was given.

```
2016/11/24 10:08:08 filter expression is invalid: requesttime>0.5
```

But it is possible to miss an error message when many ltsv lines are processed.
Because an error message is output only on startup.

sonots/lltsv