This display list was only used for texture space calculation,
and even there this display list was only used for bounding
box calulation.
Since we alreayd do have boundgind box in a curve datablock
there's no reason to duplicate non-modified display list
just to calculate bounding box later, let's just calculate
boundding box at the first point.
This makes code a little be more thread-safe but curves are
still not safe for threads at all because of bevel list and
path. That would be solved later.
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