[whatwg/streams] always check if methods are callable first (#580)

InvokeOrNoop invokes [Call](https://tc39.github.io/ecma262/#sec-call), which only takes actual functions, not anything that has `.apply` on it.
You can view, comment on, or merge this pull request online at:

  https://github.com/whatwg/streams/pull/580

-- Commit Summary --

  * always check if methods are callable first

-- File Changes --

    M reference-implementation/lib/helpers.js (9)
    M reference-implementation/test/bad-underlying-sinks.js (18)

-- Patch Links --

https://github.com/whatwg/streams/pull/580.patch
https://github.com/whatwg/streams/pull/580.diff

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