Fix fogging fog block ceiling texture in q3 maps (such as q3dm9)

I think the >= SS_BLEND0 check was added to stop transparent parts of rain splashes in ET's radar map from being fogged. Q3 expects this behavior for fog block textures though.
ET rain splash fog issue is only noticeable when using Spearmint with Q3 exp fogParms (instead of ET linear fogParms). It should be possible to fix in shader using "sort seeThrough".

Added in ioq3ztm r327.