Fixes intersection when a matrix node got several children

The picking wasn't working (see the test case below) when a matrix transform node got several children (with transform too).

When it was proceeding to the second branch, the enterNode function returned false it was still using the setCurrentTransformation from the left branch.
@jtorresfabra 

Maybe it's not optimal performance wise since the same "inverse" transformation can be applied several time.
In OSG there is a stack of intersectors which could be a little overkill. Having a stack of transformations could be a good idea, though.