fix bug for empty queue in check_accumulation()
fix bug for empty queue in check_accumulation()

cllamb0/dosenet-raspberrypi,bearing/dosenet-raspberrypi,yarocoder/dosenet-raspberrypi,tybtab/dosenet-raspberrypi,bearing/dosenet-raspberrypi,tybtab/dosenet-raspberrypi,yarocoder/dosenet-raspberrypi,cllamb0/dosenet-raspberrypi