Avoid panic when runtimes are using truncated IDs

[feiskyer]

Fix #265.

/cc @adelton @mrunalp

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In response to this:

Fix #265.

/cc @adelton @mrunalp

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[Random-Liu]

/lgtm

[adelton]

Thank you. Are the <none> <none> records without IMAGE ID expected?

# crictl images
IMAGE                               TAG                 IMAGE ID            SIZE
<none>                              <none>                                  0B
<none>                              <none>                                  0B
<none>                              <none>                                  0B
docker.io/kubernetes/pause          latest              f9d5de0795395       251kB
docker.io/library/busybox           latest              f6e427c148a76       1.36MB
registry.fedoraproject.org/fedora   27                  99b71991af6ee       246MB

Or is the fact that they don't have any IMAGE ID that bug in CRI-O which should be reported against it?

[feiskyer]

Are the records without IMAGE ID expected?

I don't think so. @mrunalp Could you verify whether this is a cri-o bug?