Fix regression from #13414

[Jarred-Sumner]

What does this PR do?

In #13414, a double deref() was added when the process has already exited by the time the stdin getter was called.

How did you verify your code works?

Regression test

[robobun]

❌ @Jarred-Sumner, your commit c29ce1d has 10 failures in #3715:

test/js/node/watch/fs.watch.test.ts - 3 failing on 🍎 14 x64

test/js/web/streams/streams.test.js - 1 failing on 🍎 13 x64

test/js/web/streams/streams.test.js - 1 failing on 🍎 14 x64

test/js/node/test/parallel/fs-watch-recursive-add-file.test.js - 1 failing on 🍎 14 x64

test/js/web/fetch/fetch-tcp-stress.test.ts - timeout on 🍎 13 aarch64

test/js/web/fetch/fetch-tcp-stress.test.ts - timeout on 🍎 14 x64

test/cli/hot/watch.test.ts - 1 failing on 🪟 x64

test/js/bun/http/fetch-file-upload.test.ts - 1 failing on 🪟 x64

test/cli/watch/watch.test.ts - 2 failing on 🪟 x64

test/js/node/test/parallel/child-process-exec-timeout-kill.test.js - 1 failing on 🍎 13 aarch64

test/js/bun/http/bun-serve-static.test.ts - annotation error on 🍎 13 aarch64

test/js/bun/http/bun-serve-static.test.ts - 1 failing on 🍎 14 aarch64