graph_blockmodel_util.hh: Improve checking

src/graph/inference/graph_blockmodel_util.hh

@@ -1139,7 +1139,7 @@ public:
         {
             auto& rs = _entries[i];
             _mes.push_back(emat.get_me(rs.first, rs.second));
-            assert(_mes.back() != emat.get_null_edge() || get<0>(_delta[i]) > 0);
+            assert(_mes.back() != emat.get_null_edge() || get<0>(_delta[i]) >= 0);
         }
         return _mes;
     }