Renderers: Make info log evaluation more robust.

[Mugen87]

Fixed #31436.

Description

Previously (see #30400), I have assumed the return value of getProgramInfoLog() and getShaderInfoLog() must always be a string. The MDN documents the return values like that.

But when looking at the WebGL spec, the return value is defined as DOMString?. So it can be null. The PR makes sure to make the call of getShaderInfoLog() and getProgramInfoLog() more safe by testing for null/undefined and use an empty string in that case. Subsequent code can then work as usual.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	338.01 78.83	338.04 78.86	+30 B +27 B
WebGPU	557.92 154.36	557.93 154.37	+12 B +6 B
WebGPU Nodes	556.84 154.16	556.85 154.17	+12 B +6 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	469.26 113.53	469.29 113.56	+30 B +26 B
WebGPU	633.22 171.39	633.23 171.4	+12 B +5 B
WebGPU Nodes	588.35 160.71	588.37 160.71	+12 B +4 B