Renderers: Make animation modules more robust.

[Mugen87]

Fixed #33157.

Description

Makes sure the animation modules of WebGPURenderer and WebGLRenderer handle a null context more gracefully.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	359.3 85.32	359.32 85.32	+20 B +4 B
WebGPU	629.97 174.94	629.99 174.94	+22 B +5 B
WebGPU Nodes	628.55 174.69	628.57 174.69	+22 B +5 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	491.5 119.98	491.52 119.9	+20 B -80 B
WebGPU	703.2 189.89	703.22 189.89	+22 B +8 B
WebGPU Nodes	652.42 177.29	652.45 177.3	+22 B +5 B