CIT Resewn: Continued

Fixes

• Textures referenced from outside the optifine/cit folder (e.g. texture=minecraft:item/example.png) no longer show up as the missing texture. This affected potions and any other item using such a path.
• model= CITs whose model refers to an undefined texture, or to a texture that doesn't exist, no longer turn the whole item purple and black.