HTTP/2 - fix header processing

httpReply->setHeaderField does not simply append (name|value) pairs,
it first erases all entries with the same name. This is quite
wrong when we have _several_ 'Set-Cookie' headers, for example.
Found while trying to login into a facebook account :)

Task-number: QTBUG-64359
Change-Id: I51416ca3ba3d92b9414e4649e493d9cd88f6d9a0
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

src/network/access/qhttp2protocolhandler.cpp

@@ -1069,7 +1069,7 @@ void QHttp2ProtocolHandler::updateStream(Stream &stream, const HPack::HttpHeader
             QByteArray binder(", ");
             if (name == "set-cookie")
                 binder = "\n";
-            httpReply->setHeaderField(name, value.replace('\0', binder));
+            httpReplyPrivate->fields.append(qMakePair(name, value.replace('\0', binder)));
         }
     }