fix(fetch): guard stream close after cancellation

lib/core/util.js

@@ -661,8 +661,7 @@
         return iterator.next().then(({ done, value }) => {
           if (done) {
             return queueMicrotask(() => {
-              controller.close()
-              controller.byobRequest?.respond(0)
+              readableStreamClose(controller)
             })
           } else {
             const buf = Buffer.isBuffer(value) ? value : Buffer.from(value)

test/fetch/readable-stream-from.js

@@ -27,3 +27,38 @@ test('ReadableStream empty enqueue', async (t) => {
   const response = new Response(iterable)
   t.assert.deepStrictEqual(await response.text(), '')
 })
+
+// https://github.com/nodejs/undici/issues/5715
+test('ReadableStream cancellation while iterator.next() is in flight', async (t) => {
+  let resolveNext
+  let startNext
+  const nextStarted = new Promise((resolve) => {
+    startNext = resolve
+  })
+  const iterable = {
+    [Symbol.asyncIterator] () {
+      return {
+        next () {
+          startNext()
+          return new Promise((resolve) => {
+            resolveNext = resolve
+          })
+        },
+        return () {
+          return Promise.resolve({ done: true, value: undefined })
+        }
+      }
+    }
+  }
+
+  const reader = new Response(iterable).body.getReader()
+  const read = reader.read()
+  await nextStarted
+  await reader.cancel()
+  resolveNext({ done: true, value: undefined })
+  t.assert.deepStrictEqual(await read, { done: true, value: undefined })
+
+  // Let the microtask that closes the controller run. It must not throw if
+  // cancellation already closed the stream.
+  await new Promise((resolve) => setImmediate(resolve))
+})