Fix frustum top plane calculation

[gmodarelli]

Hello there, I've spotted a typo in the computation of the frustum top plane.
I've briefly checked the other Mesh Shading samples and there are no bugs there.

Cheers :)

[walbourn]

Can you provide a description of how to repro the failure?

[gmodarelli]

Hey there, sorry I missed this message. Yes, I'll try to add a "Freeze Render" option so you can see how meshes outside of the top plane of the frustum are not culled.

Is it enough if I provide screenshots of this or would you like me to commit the code as well?

[stanard]

I already merged this change. Coincidentally, we found the same bug in a branch of MiniEngine and already fixed it with the same change. There is symmetry with each of the opposing planes (add/subtract), and by inspection, you can see that there was a typo on one of the planes.

[walbourn]

We ported this fix to the ATG samples copy as well and were able to repro the original issue to verify the fix. Looks good.