fix GC safety bug when walking stack
fix GC safety bug when walking stack

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