18.104.22.168: fix null broadcast-streams as RUN-PROGRAM output streams
Regression from 22.214.171.124.
Since they have element-type T, COPY-DESCRIPTOR-TO-STREAM complains
about them -- but it's more efficient to special-case them to the
null device anyways.
Also add a missing error message about unknown element types for input
...and fix numbering of RUN-PROGRAM-CAT-* tests.