Handle gss_import_cred() failure when importing gssx creds
    
    Otherwise, we might attempt to set options on a non-existent handle,
    leading to a segfault.
    
    Signed-off-by: Robbie Harwood <rharwood@redhat.com>
    Reviewed-by: Simo Sorce <simo@redhat.com>
    Merges: #244