In Node.js, stdio pipes are created before the OS spawn call, so
child.stdout/stderr/stdin are valid stream objects even when spawn
fails (e.g. ENOENT). Deno's implementation only created these after
a successful Deno.Command().spawn(), leaving them as null on failure.

This caused crashes when code accessed child.stdout after a failed
spawn, which is valid and expected in Node.js.

Now when spawn fails, we create the stdio streams, emit the error,
then destroy the streams in the next tick so the 'close' event fires
correctly (matching Node.js behavior of 'close' without 'exit' on
spawn failure).