read_first propagated every non-UdfNotFound error immediately, so a
DiscRead on the primary Unit_Key_RO.inf aborted instead of trying the
/AACS/DUPLICATE/ backup that AACS ships for exactly this case. Treat a
DiscRead as retriable like an absent candidate: continue to the next
path, remembering the error, and only propagate it once every candidate
has been tried (still more informative than a bare AacsNoKeys). Add
fall-through and propagate-after-exhaustion tests.
Matthew Jackson
14f97aacd6