Qt/C++ generated code crashes if response is of type string

Description

Qt/C++ code crashes during the API callback when output is cast to QString*

On Mac, this causes a fatal SIGSEGV exception in QtCore at QString::append(QString const&) + 17 according to the crash log.

Swagger-codegen version

Current version used by http://editor.swagger.io/#/ at time of posting.

Steps to reproduce

Include the following in the yaml:

      responses:
        '200':
          description: OK
          schema:
            type: string
            title: jsonData

then:

1. Generate Qt/C++ code
2. Create a slot corresponding to the callback and connect the callback signal to it
3. Instantiate the API interface class (e.g. SWGDefaultApi) and call the endpoint

Suggest a Fix

I believe the problem is this line of code:

https://github.com/swagger-api/swagger-codegen/blob/master/modules/swagger-codegen/src/main/resources/qt5cpp/api-body.mustache#L169

I believe the solution is to detect when {{returnType}} is QString* and in this case just replace the line with:

{{{returnType}}} output = &json;

I have tested this locally by replacing (in the generated code)

QString* output = static_cast<QString*>(create(json, QString("QString")));

with

QString* output = &json;