QSharedDataPointer detaches in unexpected situations

	QSharedDataPointer<foo> head;
	...
	auto node = head;
	if (!node)	// DO NOT cause detach()
	if (node == nullptr)	// causes detach()
	if (node != nullptr)	// causes detach()
	if (node)	// causes detach()

template <class T>
bool operator==(const QSharedDataPointer<T>& p, nullptr_t) { return p.constData() == nullptr; }
template <class T>
bool operator==(nullptr_t, const QSharedDataPointer<T>& p) { return p.constData() == nullptr; }

template <class T>
bool operator!=(nullptr_t, const QSharedDataPointer<T>& p) { return !!p; }
template <class T>
bool operator!=(const QSharedDataPointer<T>& p, nullptr_t) { return !!p; }