Wrong variable is being accessed for the texture of the threshold line when updating. Need to fix typos.

There's something weird going on with the config for "shadowfiend insanity gain threshold line" - it seems to reset after I set it and doesn't actually apply when testing it. The same thing also occurs with all the other color configs, except they actually do apply, but the config doesn't show up, looks like this: https://i.imgur.com/tPRiR8U.png

Reported by MicleTV on Curse.