28cd6ad coreos: show last modified only if metadata loaded

Authored and Committed by rfairley 4 years ago
    coreos: show last modified only if metadata loaded
    
    Show the last modified timestamp of the metadata only if
    metadata loaded successfully (i.e. `streamData.metadata` is
    defined).
    
    Signed-off-by: Robert Fairley <rfairley@redhat.com>