always fetch apidef from registry, ignore missing uri params
always fetch apidef from registry, ignore missing uri params

- URI params are considered to be always present, otherwise
  pyramid routing would trigger a 404 before the view is called
- Do not bind apidef to decorator instance, fetch it from
  config.registry every time it's needed
- Removed duplicate check for existing resource.body in
  prepare_json_body()

ScanPlusGmbH/pyramlson,jenner/pyramid_raml,jenner/pyramlson