`ImageDecoder.completed` promise property is not marked as handled

[saschanaz]

close() rejects the promise when the decoder is not complete, which triggers unhandled rejection handler when unhandled.

4. If [[ImageTrackList]] is empty, reject [[ready promise]] with exception. Otherwise perform these steps,

(And perhaps it should link to https://webidl.spec.whatwg.org/#reject, right now it's plaintext)

[dalecurtis]

Sorry, it's a bit hard to parse your meaning. Is your complaint that the completed and ready promises may trigger the global unhandled rejection handler? And that we should mark them as handled within the spec?

That sounds reasonable to me if so.

[saschanaz]

Exactly, yes.