Mooshrooms incorrectly display custom mushroom models

Yes, I broke the models again.

Mushrooms on the backs of mooshrooms display the "cubes" incorrectly.

It seems to lack shading and display the backs instead of the front, bit of z-fighting.

Steps to reproduce:

1. Apply a custom red mushroom model that contains cubes rather than plains, or download the debug pack
2. Spawn a mooshroom
3. Look at the mushrooms on the mooshroom's back, notice the cubes appear inside-out