fix(createIconPack): handle unresolved modules

[kripod]

When trying to build a site with a custom icon pack using the astro/tsconfigs/strict TSConfig, tsc --noEmit fails:

Error: node_modules/.pnpm/astro-icon@0.8.1/node_modules/astro-icon/lib/createIconPack.ts(18,45): error TS2345: Argument of type 'string | undefined' is not assignable to parameter of type 'string'. Type 'undefined' is not assignable to type 'string'.  ELIFECYCLE  Command failed with exit code 2.

It turns out that resolvePackage may return undefined, therefore this edge-case should be handled.

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: fd25e4ecaa5a55e463f1bf839094347c7652b66e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

| Name | Type | | ---------- | ----- | | astro-icon | Patch | | www | Patch |

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Name	Status	Preview	Comments	Updated (UTC)
api-astroicon	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Dec 5, 2023 7:38pm
astroicon	❌ Failed (Inspect)			Dec 5, 2023 7:38pm