cmd/podman/run.go: Error nicely when no image found

When no image is found, display a useful error message. Also, in imageToRef
protect against a nil image being passed.

Resolves: #553

Signed-off-by: baude <bbaude@redhat.com>

Closes: #555
Approved by: mheon
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f