Fixed: Group-animated materials cease animating after an engine reset.
Materials_AnimateAnimGroup assumed that all required variants for all materials involved in the translation will have already been prepared. This is not correct as an engine reset will invalidate all prepared variants and because the playsim thinks before rendering we must call Materials_Prepare rather than Materials_ChooseVariant.
Fixed: Group-animated materials cease animating after an engine reset.
Materials_AnimateAnimGroup assumed that all required variants for all
materials involved in the translation will have already been prepared.
This is not correct as an engine reset will invalidate all prepared
variants and because the playsim thinks before rendering we must call
Materials_Prepare rather than Materials_ChooseVariant.