When building a multi-stage image ( without `--layers` ) and a
stage contains only a base-image buildah removes the base-image
itself as part of cleanup process. This is a bug and following commit
fixes that.
Reproducer
```Dockerfile
FROM parent
FROM another-base
COPY --from=0 somefile .
```
`buildah build -t multi-stage .`
Closes: https://github.com/containers/podman/issues/20291
Signed-off-by: Aditya R <arajan@redhat.com>
Aditya R