fix thinko in addC for zero constant case
fix thinko in addC for zero constant case

lwahlmeier/avian,ucdseniordesign/avian,marcinolawski/avian,getlantern/avian,bigfatbrowncat/avian-pack.avian,marcinolawski/avian,bigfatbrowncat/avian-pack.avian,lostdj/avian,dicej/avian,bgould/avian,ucdseniordesign/avian,bigfatbrowncat/avian-pack.avian,getlantern/avian,minor-jason/avian,getlantern/avian,lwahlmeier/avian,lwahlmeier/avian,marcinolawski/avian,MaartenR/avian,MaartenR/avian,badlogic/avian,joshuawarner32/avian,minor-jason/avian,MaartenR/avian,minor-jason/avian,lwahlmeier/avian,ucdseniordesign/avian,getlantern/avian,marcinolawski/avian,lostdj/avian,lostdj/avian,badlogic/avian,bgould/avian,bgould/avian,dicej/avian,minor-jason/avian,dicej/avian,ucdseniordesign/avian,bgould/avian,joshuawarner32/avian,lostdj/avian,MaartenR/avian,badlogic/avian,joshuawarner32/avian,badlogic/avian,joshuawarner32/avian,dicej/avian,bigfatbrowncat/avian-pack.avian