Kubevirt: kubevirt: virt-controller nil-pointer dereference via malformed ephemeral volume

A flaw was found in KubeVirt. An authenticated user with permission to create Virtual Machine Instances (VMIs) can cause a Denial of Service (DoS) by submitting a virtual machine definition with an empty ephemeral volume. The virt-controller component fails to properly validate the volume configuration, leading to an unhandled exception and application crash during processing. Because the malformed definition persists in the cluster, the controller enters a continuous crash loop, disrupting virtual machine lifecycle operations across the entire environment.