Index out of range when making XMLHttpRequest call - qt

Question

I'm facing an error I don't really understand.
var http = new XMLHttpRequest();
var url = "http://..........";
http.open("GET", url, true);
http.onreadystatechange = function() {
console.log("readyState=" + http.readyState);
if (http.readyState == 4) {
if (http.status == 200) {
console.log("ok");
} else {
console.log("not ok");
}
}
}
http.send();
QtCreator console log:
qml: readyState=2
qml: readyState=3
ASSERT failure in QList::at: "index out of range", file C:\Qt\5.5\mingw492_32\include/QtCore/qlist.h, line 510
In Wireshark, the request is made as expected and the page correctly downloaded. What am I doing wrong?
Edit:
I am trying to use same networkaccessmanager in C++ and QML.
I have a Login class to make a connection to a website. The I need to use the same manager to make other requests in QML.
I first thought the problem was about pointer or the way I call Login(), but with Wireshark, the login request and the one made via QML have the same session id. I deduced the problem was not that, but i'm probably wrong.
main.cpp
QQmlApplicationEngine engine;
.....
QNetworkAccessManager *networkmanager = new QNetworkAccessManager();
networkmanager = engine.networkAccessManager();
Login login(networkmanager);
login.h
.....
class Login : public QObject
{
Q_OBJECT
public:
explicit Login(QNetworkAccessManager *manager, QObject *parent = 0);
.....
private:
QNetworkAccessManager *m_manager;
.....
}
login.cpp
.....
Login::Login(QNetworkAccessManager *manager, QObject *parent) : QObject(parent)
{
m_manager = manager;
connect(m_manager, SIGNAL(finished(QNetworkReply*)), this, SLOT(slotRequestFinished(QNetworkReply*)));
}
.....