KCM: Fall back to using the first ccache if the default does not exist
    
    Resolves:
    https://pagure.io/SSSD/sssd/issue/3838
    
    KCM stores the default ccache in a separate DB entry. If the DB entry
    contains a UUID that cannot be found in the DB for whatever reason, we
    should just use the first ccache as the default. (This is what we
    already do if there is no default)
    
    Reviewed-by: Pavel Březina <pbrezina@redhat.com>
    (cherry picked from commit 6bf5bcad6b9c5fb5fd867cbb094fef2a02ebf22d)