fix: ignore invalid values in npm registry JSON

[dsherret]

For denoland/deno#23862

> deno run --reload index.ts
error: failed reading lockfile 'V:\scratch\deno.lock'

Caused by:
    Error getting response at https://registry.npmjs.org/urllib for package "urllib": invalid type: map, expected a string at line 1 column 24565
> ../deno/target/debug/deno run --reload index.ts
┌ ⚠️  Deno requests env access.
├ Run again with --allow-env to bypass this prompt.
└ Allow? [y/n/A] (y = yes, allow; n = no, deny; A = allow all env permissions) >