segment is undefined client side on error page

[nikse]

Describe the bug
A clear and concise description of what the bug is.

The segment variable is undefined on client side (defined on server side) in the _layout.svelte file when rendering the _error.svelte file

Logs
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To Reproduce
To help us help you, if you've found a bug please consider the following:

Run sapper starter template and navigate to /a with the following code in _layout.svelte

export let segment;
console.log(segment) // ssr: "a", client: undefined

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• Reproductions should be small, self-contained, correct examples – http://sscce.org.

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Expected behavior
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Client side segment should have the same value as the server side

Stacktraces
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Stack trace

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Information about your Sapper Installation:

• Your browser and the version: (e.x. Chrome 52.1, Firefox 48.0, IE 10)

• Your operating system: (e.x. OS X 10, Ubuntu Linux 19.10, Windows XP, etc)

• Your hosting environment: (i.e. Local, GCP, AWS, Now, etc...)

• Sapper version (Please check you can reproduce the issue with the latest release!)

• Svelte version (Please check you can reproduce the issue with the latest release!)

• If it is an exported (npm run export) or dynamic application.

• Whether your application uses Webpack or Rollup

Severity
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Additional context
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[Conduitry]

Approximately a duplicate of #948 and a few other related issues.