Fix GUI popup's Post Effect FovX value

[DoobesURU]

Small fix to adjust the FovX formula in the Post Effects Mod to make GUIs the proper width in-game.

[DoobesURU]

So far, I have tested this fix on the several GUIs in Kirel and the few in BaronCityOffice and they all look correct with this new math.

[dpogue]

I tested this and it works, and seems to fix some horizontal compressing that happens with the default GUI cameras

[Hoikas]

I'm really curious why this fudge factor is needed. In my testing, it's unnesecary, and the max plugin doesn't do anything like this IIRC. It would be nice to have a blend file that I could look at to see what's going on... I would hate for us to merge this fudge factor to fix one case but break another when we should really be fetching this value from somewhere else.

[Jrius]

I don't know about MOUL, but at least for PotS this likely needs the same fix as regular cameras : widescreen fix. Cyan messed up their FOVs everywhere.
In PotS GUIs usually all have the same low FOV so the distortion isn't as noticeable but it's always been there. Drizzle's widescreen mod fixes this, and it makes the KI a bit rounder from what I remember.