minor cleanup and refactoring of fillBatches()
minor cleanup and refactoring of fillBatches()

marian-nmt/marian-train,emjotde/Marian,emjotde/Marian,emjotde/amunn,emjotde/amunmt,marian-nmt/marian-train,emjotde/amunn,emjotde/amunmt,amunmt/marian,marian-nmt/marian-train,marian-nmt/marian-train,marian-nmt/marian-train,emjotde/amunmt,amunmt/marian,emjotde/amunmt,emjotde/amunn,emjotde/amunn,amunmt/marian