* Fix GLTFExporter.js by checking if attenuation distance is set

Having no attenuation distance set in the project/code, defaults to infitity. This property then cannot be set in GLTF file and automatically sets to NULL. NULL property cannot be read by various softwares, for example - Blender 4 - > onwards.

By adding check if distance is !== infinity we either send that parameter if its set, or don't send it if its default.

* Update GLTFExporter.js

Clean up.

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Co-authored-by: Michael Herzog <michael.herzog@human-interactive.org>