bug: 0-softness flex prim LOD bias too high

Steps to reproduce the bug: Create a flat (z-axis) flex prim with 0 softness and zoom camera in/out centered on it.

Observed results: When the camera comes within ~5m of such a prim prim, the LOD is too extreme and quickly reduces the prim to a very simple shape. Changing object LOD in prefs has no effect either.

If the prim is very thin and from 0-.35m long (z-axis), the LOD mangles the shape, too.

Expected results: 0-softness flex prim LOD should not be so extreme.

Yes, I believe this is a manifestation of a bug in the interpolation mechanism (not the LOD itself). There should be no popping because the 0 softness flexible object has only one simulated segment always, and increased LOD is just an interpolation.

I intend to fix this before the 1.9.1 release.