try expressions doesn't work inside routes
```nim
import json, jester

routes:
  post "/":
    let input =
      try:
        request.body.parseJson()
      except:
        resp Http400
```

Got:

```
test.nim(7, 21) Error: expression 'parseJson(body(request))' is of type 'JsonNode' and has to be discarded
```

I'm on jester 0.4.3 with nim devel.