TSL: Check for undefined in uniform().

[Mugen87]

Fixed #32182.

Description

uniform() currently uses this check ( value.node && value.node.value ). This check does not properly handle the case when value.node.value is 0 (a valid value). The PR changes the check by testing for undefined.

@sunag Do we also have to honor null?

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	355.14 86.33	355.14 86.33	+0 B +0 B
WebGPU	609.62 170.99	609.66 171	+37 B +19 B
WebGPU Nodes	608.23 170.72	608.26 170.74	+37 B +21 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	486.77 121.07	486.77 121.07	+0 B +0 B
WebGPU	678.47 186.28	678.51 186.29	+37 B +14 B
WebGPU Nodes	620.47 169.54	620.5 169.56	+37 B +14 B