TypeError: Function.prototype.apply was called on null, which is a object and not a function

[BobNobrain]

Bug Description

Looks like the same bug as in #1327, but with stream and not request

Reproducible By

const {MockAgent, stream} = require('undici');
const {Writable} = require('stream');

async function main() {
    const mockAgent = new MockAgent();

    mockAgent.disableNetConnect();
    mockAgent
        .get('http://localhost')
        .intercept({
            path: '/'
        })
        .reply(200, 'ok')
        .delay(100);

    const parts = [];
    const ac = new AbortController();

    setTimeout(() => ac.abort('nevermind'), 50);

    try {
        await stream('http://localhost/', {
            opaque: {parts},
            signal: ac.signal,
            dispatcher: mockAgent
        }, ({opaque: {parts}}) => {
            return new Writable({
                write(chunk, _encoding, callback) {
                    parts.push(chunk);
                    callback();
                }
            });
        });

        console.log(Buffer.concat(parts).toString('utf-8'));
    } catch (error) {
        console.error('aborted', error);
    }
}

main().catch((e) => {
    console.error('fatal', e);
    process.exit(3);
});

Expected Behavior

Should only log RequestAbortedError and exit with 0

Logs & Screenshots

$ node repro.js
aborted RequestAbortedError [AbortError]: Request aborted
    at abort (project/node_modules/undici/lib/api/abort-signal.js:11:18)
    at AbortSignal.self.<computed> (project/node_modules/undici/lib/api/abort-signal.js:30:5)
    at AbortSignal.[nodejs.internal.kHybridDispatch] (node:internal/event_target:736:20)
    at AbortSignal.dispatchEvent (node:internal/event_target:678:26)
    at abortSignal (node:internal/abort_controller:292:10)
    at AbortController.abort (node:internal/abort_controller:323:5)
    at Timeout._onTimeout (project/repro.js:19:25)
    at listOnTimeout (node:internal/timers:559:17)
    at processTimers (node:internal/timers:502:7) {
  code: 'UND_ERR_ABORTED'
}
node:async_hooks:203
        ReflectApply(fn, thisArg, args);
        ^

TypeError: Function.prototype.apply was called on null, which is a object and not a function
    at StreamHandler.runInAsyncScope (node:async_hooks:203:9)
    at StreamHandler.onHeaders (project/node_modules/undici/lib/api/api-stream.js:107:18)
    at handleReply (project/node_modules/undici/lib/mock/mock-utils.js:278:13)
    at Timeout._onTimeout (project/node_modules/undici/lib/mock/mock-utils.js:247:7)
    at listOnTimeout (node:internal/timers:559:17)
    at processTimers (node:internal/timers:502:7)
$ echo $?
1

Environment

node: v16.20.1
OS: Darwin Kernel Version 21.6.0

Additional context

Probably should be fixed the same way, but in api-stream.js