don't null out array in ArrayList when size goes to zero
don't null out array in ArrayList when size goes to zero

This avoids thrashing in the case of a list which is frequently
emptied and refilled with a small number of elements.

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