fix(ext/web): `ReadableStream.from()` ignores null `Symbol.asyncIterator` (#23910)

If `@@asyncIterator` is `null` or `undefined`, it should ignores and
fallback to `@@iterator`.

Tests have been merged into WPT.
https://github.com/web-platform-tests/wpt/pull/46374

The proposal of `ReadableStream.from` uses TC39 [GetIterator][] and
[GetMethod][] within it.
GetMethod treats null as undefined.
So if `@@asyncIterator` is `null` it should be ignored and fallback to
`@@iterator`.

[GetIterator]: https://tc39.es/ecma262/#sec-getiterator
[GetMethod]: https://tc39.es/ecma262/#sec-getmethod

```bash
> deno eval "ReadableStream.from({ [Symbol.asyncIterator]: null, [Symbol.iterator]: () => ({ next: () => ({ done: true }) }) }).pipeTo(new WritableStream())"
error: Uncaught (in promise) TypeError: obj[SymbolAsyncIterator] is not a function
ReadableStream.from({ [Symbol.asyncIterator]: null, [Symbol.iterator]: () => ({ next: () => ({ done: true }) }) }).pipeTo(new WritableStream())
               ^
    at getIterator (ext:deno_web/06_streams.js:5105:38)
    at Function.from (ext:deno_web/06_streams.js:5207:22)
    at file:///D:/work/js/deno/tests/wpt/suite/$deno$eval:1:16
```

---------

Co-authored-by: Asher Gomez <ashersaupingomez@gmail.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/ext/web/06_streams.js b/ext/web/06_streams.js
index e01ece6c8..0192a54c6 100644
--- a/ext/web/06_streams.js
+++ b/ext/web/06_streams.js
@@ -5096,8 +5096,8 @@ async function* createAsyncFromSyncIterator(syncIterator) {
 // Ref: https://tc39.es/ecma262/#sec-getiterator
 function getIterator(obj, async = false) {
   if (async) {
-    if (obj[SymbolAsyncIterator] === undefined) {
-      if (obj[SymbolIterator] === undefined) {
+    if (obj[SymbolAsyncIterator] == null) {
+      if (obj[SymbolIterator] == null) {
         throw new TypeError("No iterator found");
       }
       return createAsyncFromSyncIterator(obj[SymbolIterator]());
@@ -5105,7 +5105,7 @@ function getIterator(obj, async = false) {
       return obj[SymbolAsyncIterator]();
     }
   } else {
-    if (obj[SymbolIterator] === undefined) {
+    if (obj[SymbolIterator] == null) {
       throw new TypeError("No iterator found");
     }
     return obj[SymbolIterator]();