startDaemon(): Detect if the daemon crashes before creating the socket (backport #12499)

[mergify]

Motivation

This avoids timeouts like those seen in https://github.com/NixOS/nix/actions/runs/13376958708/job/37358120348?pr=6962.

Context

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This is an automatic backport of pull request #12499 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 11c42cb has failed:

On branch mergify/bp/2.18-maintenance/pr-12499
Your branch is up to date with 'origin/2.18-maintenance'.

You are currently cherry-picking commit 11c42cb2e.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   tests/functional/common/functions.sh

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[Ericson2314]

@edolstra I am surprised this backport is failing

[edolstra]

Let's close this, not really important enough to backport.