Issue:
When user edit an empty VDDK image, they can remove the empty flag, without adding a valid image

how to reproduce:
a. create a provider with empty vddk
b. in the provider details page, start editing the vddk, and remove the flag without editing the vddk image url

expected:
Can't save the provider change, because the url is empty

what happen:
You can save empty vddk url, while the "empty flag" is off

URL: https://github.com/kubev2v/forklift-console-plugin/issues/1212