Possible UB in QSharedPointer::create?

QSharedPointer<T>::create calls ExternalRefCountWithContiguousData<T>::create. In there, memory for a ExternalRefCountWithContiguousData<T> object is obtained, then a ExternalRefCountData (the base class) is constructed in that storage.

This smells of UB, as we've never actually created/started the lifetime of a ExternalRefCountWithContiguousData<T>.