Baking some projects failed with "Cannot read properties of undefined (reading
'isShaderMaterial')". GLTFExporter reads material.isShaderMaterial unconditionally,
so a renderable (Mesh / Line / Points) with no material crashes the export — and a
non-Mesh renderable slips past both the isMesh prune check and material conversion.
Guard it in pruneNonRenderableMeshes: a material-less renderable is dropped if it's
a leaf, or neutralised (empty geometry + a hidden placeholder material) if it has
children so its subtree survives. Post-FX disable now lets these scenes reach the
exporter, which is why it surfaced.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
