Fix cleargrads and zerograds for uninitialized parameters
Fix cleargrads and zerograds for uninitialized parameters

wkentaro/chainer,keisuke-umezawa/chainer,hvy/chainer,okuta/chainer,cupy/cupy,wkentaro/chainer,cupy/cupy,ktnyt/chainer,cupy/cupy,chainer/chainer,kiyukuta/chainer,jnishi/chainer,anaruse/chainer,hvy/chainer,delta2323/chainer,hvy/chainer,jnishi/chainer,okuta/chainer,niboshi/chainer,jnishi/chainer,keisuke-umezawa/chainer,ronekko/chainer,chainer/chainer,niboshi/chainer,kashif/chainer,keisuke-umezawa/chainer,aonotas/chainer,hvy/chainer,ysekky/chainer,wkentaro/chainer,chainer/chainer,rezoo/chainer,pfnet/chainer,jnishi/chainer,okuta/chainer,wkentaro/chainer,keisuke-umezawa/chainer,okuta/chainer,niboshi/chainer,cupy/cupy,ktnyt/chainer,ktnyt/chainer,niboshi/chainer,chainer/chainer,ktnyt/chainer,tkerola/chainer