Why do the k3s system images have additional <none> entries in the image list?

[jandubois]

From @rak-phillip in #2626 (comment)

I think filtering out the images is a fine approach for now but I still have this slight concern that there might be some underlying issue that we'll end up glossing over. For what reason could these images that are none or empty be dangling? Why does it seem to occur only for rancher images? Why does this only appear to be an issue with containerd?