Fix mesh importer mis-exporting the offsets of some joint segments

[adamkewley]

Reported by Arash Razmjoo (github handle unknown). Model file has not been released, so I am holding it in my private collection under the handle bsm_EllipRadMod.

Prerequisites:

• Model loads fine in model editor
• Model loads fine in OpenSim GUI 4.5
• Model imports fine in mesh importer

Issue:

• After importing it into the mesh importer, it mis-exports when exporting the mesh importer scene to the model editor workflow

Screenshots:

Imports fine into model editor (arm positions are wrong, but this is a modelling error/feature, not an engine one):

Imports fine into mesh importer:

Exporting from the mesh importer produces an invalid model:

[adamkewley]

Kicking this back to next month's/February's release: investigating it requires manually slicing up the model to isolate exactly where the issue is introduced by the mesh importer.