Report the number of tasks in use when the overflow happened

src/scheduler.c

@@ -772,8 +772,8 @@ struct task *scheduler_addtask(struct scheduler *s, enum task_types type,
   const int ind = atomic_inc(&s->tasks_next);
 
   /* Overflow? */
-  if (ind >= s->size) error("Task list overflow. Need to increase "
-                            "Scheduler:tasks_per_cell.");
+  if (ind >= s->size) error("Task list overflow (%d). Need to increase "
+                            "Scheduler:tasks_per_cell.", ind);
 
   /* Get a pointer to the new task. */
   struct task *t = &s->tasks[ind];