WebGPU: Fix crash when processing a env cube

[Popov72]

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[bjsplat]

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[bjsplat]

Snapshot stored with reference name:
refs/pull/16238/merge

Test environment:
https://snapshots-cvgtc2eugrd3cgfd.z01.azurefd.net/refs/pull/16238/merge/index.html

To test a playground add it to the URL, for example:

https://snapshots-cvgtc2eugrd3cgfd.z01.azurefd.net/refs/pull/16238/merge/index.html#WGZLGJ#4600

Links to test babylon tools with this snapshot:

https://playground.babylonjs.com/?snapshot=refs/pull/16238/merge
https://sandbox.babylonjs.com/?snapshot=refs/pull/16238/merge
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[bjsplat]

WebGL2 visualization test reporter:

https://snapshots-cvgtc2eugrd3cgfd.z01.azurefd.net/refs/pull/16238/merge/testResults/webgl2playwright/index.html

[bjsplat]

Visualization tests for WebGPU

https://snapshots-cvgtc2eugrd3cgfd.z01.azurefd.net/refs/pull/16238/merge/testResults/webgpuplaywright/index.html