Previously parsing a node caused the skin that was attached to it
to be parsed, which caused the skins node joints to be parsed,
which could cause the skin to be re-parsed leading to infinite or
at the very least exponential recursion.
The fix is to just get a reference to a temporarily uninitialized
skin as they were being parsed after the scene graph just to be safe
anyway. This way we avoid the recursion problem and all the references
will be valid in the end.
Malcolm Tyrrell
Matias Kangasjärvelä
kimkulling
Yingying Wang