FileLoader: Avoid undefined for members.

[Mugen87]

Related issue: -

Description

In earlier days members of classes were sometimes added in methods but not in the constructor which means they could ended up as undefined.

It is easier to follow the code if members are always defined in the constructor and get proper default values.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	336.16 78.31	336.64 78.39	+486 B +82 B
WebGPU	522.64 145.1	522.64 145.1	+0 B +0 B
WebGPU Nodes	522.11 145	522.11 145	+0 B +0 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

	Before	After	Diff
WebGL	465.27 112.2	465.76 112.28	+489 B +80 B
WebGPU	593.11 160.72	593.11 160.72	+0 B +0 B
WebGPU Nodes	548.23 150.16	548.23 150.16	+0 B +0 B