Doesn't handle `ostree refs --delete /ostree/container/blob`

[cgwalters]

Sometimes I purge cached state with ostree refs --delete, and bootc fails in this case with e.g.

$ bootc update
ERROR Upgrading: Computing status: Booted deployment: Reading deployment metadata: Missing base image ref ostree/container/blob/sha256_3A_bc1c4880a644626096a0c60c25738a36e40d5700792094e89a2bad4ce9c70872

Yet rpm-ostree succeeds because it is resilient to missing state; we just need to do the same.

[vrothberg]

Can we translate the issue into actionable items? I may miss the obvious because I haven't looked in the code base for a long time.