Invalid pointer return with QGridLayout::itemAt(-1)

inline QLayoutItem *itemAt(int index) const {
    if (index < things.count())
        return things.at(index)->item();
    else
        return 0;
}
inline QLayoutItem *takeAt(int index) {
    Q_Q(QGridLayout);
    if (index < things.count()) {
        if (QGridBox *b = things.takeAt(index)) {
            QLayoutItem *item = b->takeItem();
            if (QLayout *l = item->layout()) {
                // sanity check in case the user passed something weird to QObject::setParent()
                if (l->parent() == q)
                    l->setParent(0);
            }
            delete b;
            return item;
        }
    }
    return 0;
}