Fixed null secondary colour in setPrimaryColorIndex
Fixed null secondary colour in setPrimaryColorIndex

- fixed null secondary colour in setPrimaryColorIndex with different
numbers of secondary colours per primary colour
- changed setPrimaryColorIndex to use getRandomSecondaryColorIndexFor
helper if secondary colour no longer valid
- changed nextPrimaryColorIndex to use getRandomSecondaryColorIndexFor
helper
- implemented next_primary_color and next_secondary_color

UberEnt/pa-server-script