Fix bug in child list

src/libtree.cpp

@@ -29,7 +29,7 @@ template <class Real, Integer DIM> class ParticleTreeWrapper {
         node_ghost_[i] = node_attr_[i].Ghost;
         node_leaf_ [i] = node_attr_[i].Leaf;
         parent_lst_[i] = -1;
-        child_lst_ [i] = -1;
+        for (Integer j = 0; j < MAX_CHILD; j++) child_lst_[i*MAX_CHILD+j] = -1;
       }
       for (Long i = 0; i < Nnodes; i++) { // Set parent_lst, child_lst_
         Integer depth = node_mid_[i].Depth();