fix(ext/fetch): support empty formdata (denoland#16165)

This PR adds support for empty `FormData` parsing in
`Response`/`Request`

```js
new Response(new FormData()).formData()
```

ref: web-platform-tests/wpt#28607

ext/fetch/21_formdata.js

@@ -393,9 +393,19 @@
  * @returns {FormData}
  */
  parse() {
- // Body must be at least 2 boundaries + \r\n + -- on the last boundary.
+ // To have fields body must be at least 2 boundaries + \r\n + --
+ // on the last boundary.
  if (this.body.length < (this.boundary.length * 2) + 4) {
- throw new TypeError("Form data too short to be valid.");
+ const decodedBody = core.decode(this.body);
+ const lastBoundary = this.boundary + "--";
+ // check if it's an empty valid form data
+ if (
+ decodedBody === lastBoundary ||
+ decodedBody === lastBoundary + "\r\n"
+ ) {
+ return new FormData();
+ }
+ throw new TypeError("Unable to parse body as form data.");
  }
 
  const formData = new FormData();

tools/wpt/expectation.json

@@ -3077,14 +3077,8 @@
  "response-static-json.any.worker.html": true
  },
  "body": {
- "formdata.any.html": [
- "Consume empty response.formData() as FormData",
- "Consume empty request.formData() as FormData"
- ],
- "formdata.any.worker.html": [
- "Consume empty response.formData() as FormData",
- "Consume empty request.formData() as FormData"
- ],
+ "formdata.any.html": true,
+ "formdata.any.worker.html": true,
  "mime-type.any.html": true,
  "mime-type.any.worker.html": true
  },
@@ -3231,14 +3225,8 @@
  "response.text() rejects if already aborted",
  "Call text() twice on aborted response"
  ],
- "request.any.html": [
- "Calling formData() on an aborted request",
- "Aborting a request after calling formData()"
- ],
- "request.any.worker.html": [
- "Calling formData() on an aborted request",
- "Aborting a request after calling formData()"
- ],
+ "request.any.html": true,
+ "request.any.worker.html": true,
  "cache.https.any.html": false,
  "cache.https.any.worker.html": false
  }