(Area query) Guiding box finder: Can go from leaf upwards, instead of root downwards

The "guiding box finder" step of the area query has to descend the tree structure in order to find the guiding box that contains the ball center. If we are in a situation where we know in what leaf the ball center is located it, it may be advantageous to start instead at the leaf. Since one of the ancestors of the leaf must be the guiding box, we only have to look at the leaf's ancestor chain. This results in looking at fewer boxes than a traversal, especially if the ball radius is small.