anari: fix crash on curves without primitive.index or vertex.radius - #87

primitive.index and vertex.radius are optional on curve geometry (only vertex.position is required in KHR_GEOMETRY_CURVE, which barney advertises), but barney/anari/Geometry.cpp dereferences both without a null check:

• Curve::setBarneyParameters() reads m_index->totalSize() (line 636). A curve without an index segfaults on the first render, or on the first world bounds query, since that builds the model too.
• Curve::bounds() reads m_vertexRadius->beginAs<float>() (line 669). A curve that relies on the global radius segfaults when the world bounds are queried.

The ANARI SDK's test/random_curves scene, which has an unindexed curve with a global radius, crashes on both lines. So does this minimal pynari case:

geom = device.newGeometry('curve')
geom.setParameter('vertex.position', anari.ARRAY1D,
                  device.newArray1D(anari.FLOAT32_VEC3, positions))
geom.setParameter('radius', anari.FLOAT32, .2)  # no primitive.index, no vertex.radius
geom.commitParameters()
# ... surface, world
world.getBounds()  # or frame.render(): SIGSEGV

Fix

• Without primitive.index, every vertex except the last one starts a segment, as in helide. Indexed curves are unchanged.
• Without per-vertex radii, Curve::bounds() uses the global radius, under the same condition setBarneyParameters() already uses.

unitTests/curve-optional-params.py renders such a curve and checks the world bounds and the covered pixels. It calls World.getBounds(), which is in pynari master but not in the 1.4.0 release.

Testing

I built barney_cpu (Embree backend) on macOS arm64 with Apple clang 21, against ANARI-SDK main (0.17.0). I built pynari master against the same SDK and loaded barney_cpu through ANARI_LIBRARY. I ran each case on main, with only one of the two hunks, and with the full fix:

The existing tests/*.sh still pass. I did not build or run the CUDA, OptiX or HIP backends because this machine has no GPU. The change is in the backend-independent ANARI layer.

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