Fix getHeaders crash

[khuezy]

This is a minor fix on a crash, but needs investigation later.

I tried to pipe the request instead and it works for some sites...
Need to look into https://github.com/vercel/next.js/blob/canary/packages/next/src/server/lib/router-utils/proxy-request.ts
I tried creating the stream from the request but that didn't work 🤷

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Name	Status	Preview	Comments	Updated (UTC)
open-next	❌ Failed (Inspect)			Nov 22, 2023 5:06pm