Leak in UI delegates if the root of the Component isn't an Item

[Chris Coulson]

Currently, oxide::qquick::WebPopupMenuDelegate (and others) do something like this:

QQmlContext* baseContext = component->creationContext();
context_.reset(new QQmlContext(baseContext));
item_.reset(qobject_cast<QQuickItem *>(component->beginCreate(context_.data())));

However, if the root of the Component isn't an Item, the qobject_cast here will return NULL and the result of QQmlComponent::beginCreate() will leak forever