Fix errors associated with incorrect skeleton map parsing

[ryanjsims]

The skeleton maps can have multiple remapping layers which were not being parsed correctly and caused a crash when exporting the skeleton of certain models (exosuit and others for example)

This fixes the crash but doesn't perfectly export the models with multiple remapping layers, some vertices will be associated to the wrong bone - there likely is some data that we need to use to figure out the correct skeleton map and the correct remapping layer for each vertex. It still needs more research, obviously

[ryanjsims]

You can see in this screenshot how there is some geometry attached to the knee joint that shouldn't be on the back of the mech.

[xypwn]

Seems like you're making good progress. Nice work and thanks a lot for sharing!