incremental_forward index fix
incremental_forward index fix


Former-commit-id: 1ae38d36cf2c55749f410490e92b979fa3c85125
xunzhang/dynet,xunzhang/dynet,shuheik/dynet,shuheik/dynet,clab/cnn,shuheik/dynet,clab/dynet,xunzhang/dynet,danielhers/dynet,shuheik/dynet,shuheik/dynet,danielhers/dynet,chunyang-wen/dynet,chunyang-wen/dynet,clab/dynet,clab/dynet,clab/cnn,shuheik/dynet,danielhers/dynet,danielhers/dynet,clab/dynet,chunyang-wen/dynet,xunzhang/dynet,clab/dynet,shuheik/dynet,clab/dynet,chunyang-wen/dynet,clab/cnn,danielhers/dynet,danielhers/dynet,clab/dynet,danielhers/dynet