preload doesn't work in root page (src/routes/index.html) after visiting a 404

[sgametrio]

Issue description

Navigating on root page (source at src/routes/index.html), which loads data on preload, doesn't load data (warning <Index> was created without expected data property) only after visiting a 404 page.

How to reproduce

• Clone repo
• npm install
• npm run dev
• Navigate to about route (which return 404) and click on Home to see that data is not loaded.
  Try instead to navigate to about and then blog: data is loaded there even if blog and /index.html have the same logic.

[Conduitry]

Should be fixed by sveltejs/sapper#620.