Svelte 5: `<title>` breaks if object becomes undefined

[Rich-Harris]

Describe the bug

If you have something like this...

{#if post}
  <Seo {post} />
{/if}

<script>
  let { post } = $props();
</script>

<svelte:head>
  <title>{post.title}</title>
</svelte:head>

...then if post becomes null, the {post.title} render effect updates before the component is removed.

Probably makes sense to roll the fix into the #10594 work unless the fix is trivial.

Reproduction

preview link

Logs

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System Info

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Severity

annoyance