QHttpServer HTTP chunked request body handling

Related to QTBUG-60105 (jefernan)

I have been playing a bit with QHttpServer and noticed that it does not handle the HTTP body correctly, for chunked requests - for example if I send HTTP POST, with body that is just plain binary data, the QHttpServerRequest::body() contains only the last chunk received.

Just from a quick browse through the code:

int QHttpServerRequestPrivate::onBody(http_parser *httpParser, const char *at, size_t length)
{
    qCDebug(lc) << httpParser << QString::fromUtf8(at, int(length));
    auto i = instance(httpParser);
    i->state = State::OnBody;
    i->body = QByteArray(at, int(length));
    return 0;
}

The code should probably check that part of the body was already received?