fix a bug which calls randint with empty range
fix a bug which calls randint with empty range

nusdbsystem/incubator-singa,kaiping/incubator-singa,apache/incubator-singa,ijingo/incubator-singa,ijingo/incubator-singa,nusdbsystem/incubator-singa,kaiping/incubator-singa,apache/incubator-singa,kaiping/incubator-singa,kaiping/incubator-singa,ijingo/incubator-singa,nudles/incubator-singa,nudles/incubator-singa,kaiping/incubator-singa,apache/incubator-singa,apache/incubator-singa,nusdbsystem/incubator-singa,nusdbsystem/incubator-singa,nusdbsystem/incubator-singa,ijingo/incubator-singa,ijingo/incubator-singa,nudles/incubator-singa,nudles/incubator-singa,apache/incubator-singa,nudles/incubator-singa