Better check in place to avoid invalid tasks after splittasks has been called.

src/engine.c

@@ -2976,6 +2976,14 @@ void engine_maketasks(struct engine *e) {
   /* Split the tasks. */
   scheduler_splittasks(sched);
 
+#ifdef SWIFT_DEBUG_CHECKS
+  /* Verify that we are not left with invalid tasks */
+  for (int i = 0; i < e->sched.nr_tasks; ++i) {
+    const struct task *t = &e->sched.tasks[i];
+    if (t->ci == NULL && t->cj != NULL && !t->skip) error("Invalid task");
+  }
+#endif
+
   /* Free the old list of cell-task links. */
   if (e->links != NULL) free(e->links);
   e->size_links = 0;

src/scheduler.c

@@ -935,12 +935,6 @@ struct task *scheduler_addtask(struct scheduler *s, enum task_types type,
                                enum task_subtypes subtype, int flags,
                                int implicit, struct cell *ci, struct cell *cj) {
 
-#ifdef SWIFT_DEBUG_CHECKS
-  if (ci == NULL && cj != NULL)
-    error("Added a task with ci==NULL and cj!=NULL type=%s/%s",
-          taskID_names[type], subtaskID_names[subtype]);
-#endif
-
   /* Get the next free task. */
   const int ind = atomic_inc(&s->tasks_next);