Add nil check for image status size
Add nil check for image status size

Theoretically it is possible to retrieve an image status size of zero,
which would lead into a crash on dereferencing the `status.Size`
pointer.

Signed-off-by: Sascha Grunert <70ab469ddb2ac3e35f32ed7c2fd1cca514b2e879@suse.com>

kubernetes-incubator/cri-o,kubernetes-incubator/ocid,nalind/cri-o,mikebrow/cri-o,rhatdan/cri-o,mikebrow/cri-o,kubernetes-incubator/ocid,kubernetes-incubator/ocid,nalind/cri-o,nalind/cri-o,kubernetes-incubator/cri-o,mikebrow/cri-o,kubernetes-incubator/cri-o,rhatdan/cri-o,rhatdan/cri-o,rhatdan/cri-o,mikebrow/cri-o,kubernetes-incubator/cri-o