Add result in 500 status code

Created by: gmtstephane

Hi, in the Go server, we can only have Status code 200 or 500 wether our implementation function return an error or not.

In case or error (err!=nil), the server write the status code 500 without any messages .

result, err := c.service.AddPet(*pet)
	if err != nil {
		w.WriteHeader(500)
		return
	}	
	EncodeJSONResponse(result, nil, w)

In many cases, their can be several types of error in our implementation, and i wouldlike to return the error message to the client. I suggest to Encode the response with the result variable, with the statuscode 500, which will let us write responses in case of error.

        if err != nil {
		statusCode := 500
		EncodeJSONResponse(result, &statusCode, w)
		return
	}

@antihax (2017/11) @grokify (2018/07) @kemokemo (2018/09) @bkabrda (2019/07) @wing328

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