generateSW disables default error page

[jasoneliu]

In production, when using export const prerender = true and generateSW, SvelteKit's default error page no longer works. Instead, the user is shown the page at /.

Reproduction:

• In examples/sveltekit-ts, update package.json to use "@vite-pwa/sveltekit": "^0.2.1"
• Run npm i, npm run build, and npm run preview
• Visit http://localhost:4173/. This shows +page.svelte as expected.
• Visit http://localhost:4173/about. This shows about/+page.svelte as expected.
• Visit http://localhost:4173/oops. This shows +page.svelte instead of rendering the default error page.

This issue does not occur in development. When running npm run dev and visiting http://localhost:5173/oops, it shows the default error page.

I'm using Node v16.19.0 and npm v8.19.3.