minecraft: fix rotation over z axis

When a model (e.g. a torch on a wall) has a rotation over the z axis, we
were rotating the model the wrong way around.

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I noticed this while using this on my usual world. All the torches on the wall were going *into* the wall instead of away from it.

I think this is the right place to fix it, since AFAICT this is where we transform minecraft axes into the model which hematite uses, but I was never that good at geometry.