added missing always open root node statement (a regression)

src/fof/fof_nearest.cc

@@ -157,6 +157,14 @@ class fofdata_comm : public generic_comm<fofdata_in, fofdata_out, T_tree, T_doma
 
                 fofnode *current = Tree->get_nodep(no, shmrank);
 
+                if(current->level == 0)
+                  {
+                    /* we always open the root node (its full node length can't be stored in the integer type */
+                    no      = current->nextnode; /* no change in shmrank expected here */
+                    shmrank = current->nextnode_shmrank;
+                    continue;
+                  }
+
                 int nosaved = no;
 
                 no      = current->sibling; /* in case the node can be discarded */