ItemHeaderAt
if (const ItemHeader *header = ItemHeaderAt(0))
if (const ItemHeader *header = ItemHeaderAt(CountItems() - 1))
const ItemHeader *ItemHeaderAt(int32 index) const;
error = SetTo(node, node->ItemHeaderAt(index));
node->ItemHeaderAt(0)->GetKey(&lowerKey);
node->ItemHeaderAt(mid)->GetKey(&midKey);