Model fails to import since extras property is only partially parsed

[hybridherbst]

This fails completely:
kid.glb.zip

[hybridherbst]

Looks like there's incorrect parsing of the mesh going on: instead of parsing the "extras" property as part of the array deserializerFunc, the loop repeats for all sub properties of extras, passing them to the deserializerFunc which ends up creating empty primitives with no attributes at all.

So two bugs:

• empty primitives/no attributes result in exceptions – not sure if that is valid glTF but I think an uncaught exception is still not good
• parsing is wrong in MeshPrimitive.Deserialize

[hybridherbst]

Turns out this was related: KhronosGroup/glTF#1036
The primitives.extra property was parsed for targetNames, but not in a correct way, so nested objects as primitives.extra messed up the import.

[hybridherbst]

Fixed on dev