Fix bug when hyp_length == 0
Fix bug when hyp_length == 0

Proyag/nematus,yang1fan2/nematus,shuoyangd/nematus,shuoyangd/nematus,shuoyangd/nematus,Proyag/nematus,EdinburghNLP/nematus,cshanbo/nematus,cshanbo/nematus,rsennrich/nematus,cshanbo/nematus,EdinburghNLP/nematus,Proyag/nematus,cshanbo/nematus,cshanbo/nematus,EdinburghNLP/nematus,rsennrich/nematus,shuoyangd/nematus,cshanbo/nematus,yang1fan2/nematus,Proyag/nematus,yang1fan2/nematus,yang1fan2/nematus,yang1fan2/nematus,yang1fan2/nematus,rsennrich/nematus,yang1fan2/nematus,EdinburghNLP/nematus,Proyag/nematus,rsennrich/nematus,EdinburghNLP/nematus,shuoyangd/nematus,yang1fan2/nematus,rsennrich/nematus,yang1fan2/nematus,Proyag/nematus,rsennrich/nematus,yang1fan2/nematus,EdinburghNLP/nematus,shuoyangd/nematus