Short-circuit checking of NULL version specifications.

;;;; version-satisfies

(with-upgradability ()

  ;; short-circuit testing of null version specifications.

  ;; this is an all-pass                  

  (defmethod version-satisfies :around ((c t) (version null))

    (declare (ignorable c version))

    t)

  (defmethod version-satisfies ((c component) version)

    (unless (and version (slot-boundp c 'version) (component-version c))

      (when version