BUG/MEDIUM: task: Don't forget to decrement max_processed after each task.

When the task list was introduced, we bogusly lost max_processed--, that means
we would execute as much tasks as present in the list, and we would never
set active_tasks_mask, so the thread would go to sleep even if more tasks were
to be executed.

1.9-dev only, no backport is needed.

src/task.c

@@ -367,6 +367,7 @@ void process_runnable_tasks()
 				task_queue(t);
 		}
 
+		max_processed--;
 		if (max_processed <= 0) {
 			active_tasks_mask |= tid_bit;
 			activity[tid].long_rq++;