fix missing packet access check
fix missing packet access check

chunyang-wen/dynet,clab/dynet,clab/dynet,danielhers/dynet,danielhers/dynet,shuheik/dynet,clab/dynet,shuheik/dynet,xunzhang/dynet,shuheik/dynet,clab/cnn,shuheik/dynet,shuheik/dynet,chunyang-wen/dynet,danielhers/dynet,shuheik/dynet,chunyang-wen/dynet,clab/dynet,clab/dynet,xunzhang/dynet,clab/cnn,danielhers/dynet,shuheik/dynet,clab/dynet,danielhers/dynet,chunyang-wen/dynet,xunzhang/dynet,clab/dynet,clab/cnn,xunzhang/dynet,danielhers/dynet,danielhers/dynet