QQmlComponentPrivate::doBeginCreate can crash in some scenarios

QQmlEnginePrivate::rootContext

can be null in some cases when calling:

QObject *QQmlComponentPrivate::doBeginCreate(QQmlComponent *q, QQmlContext *context)

https://github.com/qt/qtdeclarative/blob/4ddbef67357275ba6f100ce028a81c92405720b7/src/qml/qml/qqmlcomponent.cpp#L335

Causing this line to crash:

https://github.com/qt/qtdeclarative/blob/4ddbef67357275ba6f100ce028a81c92405720b7/src/qml/qml/qqmlcomponent.cpp#L1014

One example of this flow is as follows:

QQmlEngine deletes the rootContext in its destructor and invalidates the typeLoader:

https://github.com/qt/qtdeclarative/blob/4ddbef67357275ba6f100ce028a81c92405720b7/src/qml/qml/qqmlengine.cpp#L565
 
Which calls:

void QQmlTypeLoader::shutdownThread()
{    
    if (m_thread && !m_thread->isShutdown())
        m_thread->shutdown(); //QQmlThread::shutdown()
} 

 
The QmlThread processes any events left in the list, some of which can be related to asynchronous component creation e.g.

QQmlComponentPrivate::typeDataReady(QQmlTypeData *) override;

Which triggers a "QQmlComponent::statusChanged" signal to "QQmlComponent::Ready"

If the end user is still connected, they may attempt to finish creating the component with "QQmlComponent::create(nullptr)" (use rootContext as context) leading us to the crash described at the start.

Example project of the crash is attached