SSAO2: Don't clear post processes if not necessary

[Popov72]

No description provided.

[bjsplat]

Please make sure to label your PR with "bug", "new feature" or "breaking change" label(s).
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[bjsplat]

Snapshot stored with reference name:
refs/pull/15085/merge

Test environment:
https://babylonsnapshots.z22.web.core.windows.net/refs/pull/15085/merge/index.html

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

https://babylonsnapshots.z22.web.core.windows.net/refs/pull/15085/merge/index.html#WGZLGJ#4600

Links to test babylon tools with this snapshot:

https://playground.babylonjs.com/?snapshot=refs/pull/15085/merge
https://sandbox.babylonjs.com/?snapshot=refs/pull/15085/merge
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https://nme.babylonjs.com/?snapshot=refs/pull/15085/merge

To test the snapshot in the playground with a playground ID add it after the snapshot query string:

https://playground.babylonjs.com/?snapshot=refs/pull/15085/merge#BCU1XR#0

[bjsplat]

WebGL2 visualization test reporter:

https://babylonsnapshots.z22.web.core.windows.net/refs/pull/15085/merge/testResults/webgl2playwright/index.html

[bjsplat]

Visualization tests for WebGPU (Experimental)
Important - these might fail sporadically. This is an optional test.

https://babylonsnapshots.z22.web.core.windows.net/refs/pull/15085/merge/testResults/webgpuplaywright/index.html