not set _orderOfArrival to 0 after in visit

There may be a problem in this situation

```c++
auto node1 = Node::node();
auto node2 = Node::node();
addChild(node1);
addChild(node2);
```

`node1` will be visited before `node2` because it is added first. But after visit, _orderOfArrival of node1 and node2 are 0. And the implementation of `nodeComparisonLess` is

```c++
bool nodeComparisonLess(Node* n1, Node* n2)
{
    return( n1->getLocalZOrder() < n2->getLocalZOrder() ||
           ( n1->getLocalZOrder() == n2->getLocalZOrder() && n1->getOrderOfArrival() < n2->getOrderOfArrival() )
           );
}
```

It will return false, which means node2 will be visited before node1.