[whatwg/streams] Replace impossible condition with assert (#987)

It is not possible for
WritableStreamDefaultControllerAdvanceQueueIfNeeded to be called when
the state is "closed" or "errored". Replace the condition with an
assert.

No functional changes.
You can view, comment on, or merge this pull request online at:

  https://github.com/whatwg/streams/pull/987

-- Commit Summary --

  * Replace impossible condition with assert

-- File Changes --

    M index.bs (2)
    M reference-implementation/lib/writable-stream.js (4)

-- Patch Links --

https://github.com/whatwg/streams/pull/987.patch
https://github.com/whatwg/streams/pull/987.diff

-- 
You are receiving this because you are subscribed to this thread.
Reply to this email directly or view it on GitHub:
https://github.com/whatwg/streams/pull/987