Fix empty name problem in GLTFLoader

[drcmda]

References:

#18530 (comment)

https://spectrum.chat/react-three-fiber/general/help-required-unable-to-load-a-gltf-model~d77788d6-35ff-4e5d-b3e9-23682c661699

GLTF's can be exported with empty names, or missing names. GLTFLoader seems to have problems with the former. For instance, this is the nodes array of the following model: https://sketchfab.com/3d-models/red-city-356c773c4b9a45d8b9d4aa04c60ecb27

  ...
  { mesh: 0, name: '' },
  { mesh: 1, name: '' },
  { mesh: 2, name: '' },
  { mesh: 3, name: '' }

GLTFLoader will auto generate names, like mesh_0, mesh_1 and so on, this happens in loadMesh:

mesh.name = meshDef.name || ( 'mesh_' + meshIndex );
if ( geometries.length > 1 ) mesh.name += '_' + i;

Notice how it checks the string itself. So, by now the mesh has an actual name, but a small bug wipes it out again afterwards in the LoadNode function:

if ( nodeDef.name !== undefined ) {
  node.userData.name = nodeDef.name;
  node.name = THREE.PropertyBinding.sanitizeNodeName( nodeDef.name );
}

Here it checks against undefined, so despite the def name being empty and the auto-generated name being present, it goes in there and overwrites the name with an empty string.

I have fixed all the other places that had this problem.

[donmccurdy]

Thanks! Agreed the change.

/cc @lexaknyazev do you think empty string, "name": "", should result in a validation warning? It seems similar to null to me, but not a strong preference.

[mrdoob]

Thanks!