Don't use clear coat roughness as base roughness if clear coat is 0 (#1323)
Don't use clear coat roughness as base roughness if clear coat is 0 (#1323)

This change finds the max of the clear coat and base layer roughness
then lerps the base layer roughness according to the amount of clear
coat.
google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament