Virtqueue handler functions in device emulation code often look something like this:

while (!virtio_queue_empty(vq)) {
...pop and process virtqueue element...
}

virtio-blk, virtio-scsi, virtio-crypto, and vhost-shadow-virtqueue use this pattern.

The device may break (i.e. hit an error that requires device reset) during the loop. virtio_queue_empty() returns 1 for broken split vrings but not for broken packed vrings, leading to an infinite loop.

Adjust the packed vring behavior to match split vrings and avoid infinite loops.