Merge headers

Otherwise the headers from `JSONResponse` are gone and the Content-Type of the response would be `text/html` instead of `application/json; charset=utf-8`. This leads to broken scripts since we set the `nosniff` tag, furthermore this is very bad from a security PoV.

lib/public/appframework/controller.php

@@ -70,7 +70,7 @@ abstract class Controller {
 						$data->getData(),
 						$data->getStatus()
 					);
-					$response->setHeaders($data->getHeaders());
+					$response->setHeaders(array_merge($data->getHeaders(), $response->getHeaders()));
 					return $response;
 				} else {
 					return new JSONResponse($data);