This one was nasty, issue comes with temp/nofree CD layers that get 'removed on the fly'
from saved mesh CDData. Since mesh struct itself was written before that cleanup, it would
still have the old, invalid number of layers. That would lead to a buffer overflow when
loading data later (odd you had to do this twice (i.e. have 2 'ghost' layers) to get the crash).
New code prevents that by always making a copy of the mesh (we were already doing that mostly
anyway, since we were saving without tessfaces), copying (by ref of course) in it cddata,
and then writing mesh struct. Makes code a bit more verbose, but... it works!
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