Fill zero for py3
Fill zero for py3

Py3 cannot compare None and int.

niboshi/chainer,sinhrks/chainer,kashif/chainer,keisuke-umezawa/chainer,kikusu/chainer,ktnyt/chainer,ktnyt/chainer,delta2323/chainer,cupy/cupy,t-abe/chainer,keisuke-umezawa/chainer,AlpacaDB/chainer,rezoo/chainer,hvy/chainer,wkentaro/chainer,benob/chainer,hvy/chainer,wkentaro/chainer,ktnyt/chainer,keisuke-umezawa/chainer,minhpqn/chainer,tkerola/chainer,muupan/chainer,truongdq/chainer,tigerneil/chainer,cupy/cupy,muupan/chainer,hvy/chainer,cupy/cupy,chainer/chainer,jnishi/chainer,anaruse/chainer,benob/chainer,kiyukuta/chainer,laysakura/chainer,chainer/chainer,sinhrks/chainer,ytoyama/yans_chainer_hackathon,cemoody/chainer,truongdq/chainer,okuta/chainer,keisuke-umezawa/chainer,kikusu/chainer,niboshi/chainer,AlpacaDB/chainer,okuta/chainer,jnishi/chainer,tscohen/chainer,ktnyt/chainer,chainer/chainer,jnishi/chainer,wkentaro/chainer,niboshi/chainer,hvy/chainer,t-abe/chainer,okuta/chainer,pfnet/chainer,okuta/chainer,ronekko/chainer,ysekky/chainer,Kaisuke5/chainer,jnishi/chainer,1986ks/chainer,niboshi/chainer,aonotas/chainer,cupy/cupy,chainer/chainer,sou81821/chainer,wkentaro/chainer