* lisp/gnus/gnus-search.el (gnus-search-query-expand-key): There was a
misunderstanding about how completion-all-completion works (if the
test string can't be completed, the whole table is returned). Simplify
to use try-completion.
* test/lisp/gnus/gnus-search-tests.el (gnus-s-expand-keyword): Ensure
that an unknown/uncompletable keyword is returned unmolested.
d93ff9459f