Only create the stars ghost task when running with feedback switched on.

src/engine_maketasks.c

@@ -935,8 +935,10 @@ void engine_make_hierarchical_tasks_hydro(struct engine *e, struct cell *c) {
                             /* implicit = */ 1, c, NULL);
       engine_add_ghosts(e, c, c->hydro.ghost_in, c->hydro.ghost_out);
 
-      c->stars.ghost = scheduler_addtask(s, task_type_stars_ghost,
-                                         task_subtype_none, 0, 0, c, NULL);
+      if (with_feedback) {
+	c->stars.ghost = scheduler_addtask(s, task_type_stars_ghost,
+					   task_subtype_none, 0, 0, c, NULL);
+      }
 
 #ifdef EXTRA_HYDRO_LOOP
       /* Generate the extra ghost task. */