Re: [whatwg/streams] Discard auto-allocated BYOB request on enqueue (#1171)

@MattiasBuelens commented on this pull request.



> @@ -3136,6 +3136,13 @@ The following abstract operations support the implementation of the
      [$TransferArrayBuffer$](|firstPendingPullInto|'s [=pull-into descriptor/buffer=]).
  1. Perform ! [$ReadableByteStreamControllerInvalidateBYOBRequest$](|controller|).
  1. If ! [$ReadableStreamHasDefaultReader$](|stream|) is true
+  1. If |controller|.[=ReadableByteStreamController/[[pendingPullIntos]]=] is not
+     [=list/is empty|empty=],
+   1. Assert: |controller|.[=ReadableByteStreamController/[[pendingPullIntos]]=]'s [=list/size=]

Hang on... this is wrong. *Every call* to `ReadableStreamDefaultReader.read()` creates a new pull-into descriptor, regardless of whether we can `pull()` again. For example, this creates two such descriptors:
```javascript
let controller;
const stream = new ReadableStream({
  start(c) {
    controller = c;
  },
  type: 'bytes',
  autoAllocateChunkSize: 16
}, {
  highWaterMark: 0
});

const reader = stream.getReader();
const read1 = reader.read();
const read2 = reader.read();
```
What *is* true is that, if `autoAllocateChunkSize` is not undefined, then the length of `[[pendingPullIntos]]` matches that of `[[readRequests]]`. So we need to remove *only* the first descriptor on `enqueue()`.

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