sched: rt: dont stop the period timer when there are tasks wanting to run

So if the group ever gets throttled, it will never wake up again.

Reported-by: "Daniel K." <[e-mail]>
Signed-off-by: Peter Zijlstra <[e-mail]>
Tested-by: Daniel K. <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>

kernel/sched_rt.c

···
 			if (rt_rq->rt_time || rt_rq->rt_nr_running)
 				idle = 0;
 			spin_unlock(&rt_rq->rt_runtime_lock);
-		}
+		} else if (rt_rq->rt_nr_running)
+			idle = 0;
 
 		if (enqueue)
 			sched_rt_rq_enqueue(rt_rq);