bugfix to handling of POST/PUT calls when data is present and we can't determine the content type

This change fixes an issue where you could `POST` or `PUT` data to an end point without setting the content type to `application/json` first.  While working with the API to create a job type I forgot to set the content type prior to sending the request which caused the endpoint's code to throw an internal server error rather than a more useful error code telling me what was wrong.  The problem was `g.json` was not set properly prior to entering into the endpoint which we should expect to be set properly by our before request handler.