job.c: add missing notifier initialization

It seems that on_idle list is not properly initialized like
the other notifiers.

Fixes: 34dc97b9 ("blockjob: Wake up BDS when job becomes idle")
Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

job.c

@@ -352,6 +352,7 @@ void *job_create(const char *job_id, const JobDriver *driver, JobTxn *txn,
     notifier_list_init(&job->on_finalize_completed);
     notifier_list_init(&job->on_pending);
     notifier_list_init(&job->on_ready);
+    notifier_list_init(&job->on_idle);
 
     job_state_transition(job, JOB_STATUS_CREATED);
     aio_timer_init(qemu_get_aio_context(), &job->sleep_timer,