fix(search): handle missing description when file is not a markdown

[farnabaz]

🔗 Linked issue

resolves #2700

❓ Type of change

• [ ] 📖 Documentation (updates to the documentation or readme)
• [x] 🐞 Bug fix (a non-breaking change that fixes an issue)
• [ ] 👌 Enhancement (improving an existing functionality like performance)
• [ ] ✨ New feature (a non-breaking change that adds functionality)
• [ ] ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

📝 Checklist

• [ ] I have linked an issue or discussion.
• [ ] I have updated the documentation accordingly.

[cloudflare-workers-and-pages[bot]]

Deploying nuxt-content with    Cloudflare Pages

Latest commit:	d10a741
Status:	✅  Deploy successful!
Preview URL:	https://3ddb1bae.nuxt-content-1il.pages.dev
Branch Preview URL:	https://fix-missing-description-sear.nuxt-content-1il.pages.dev

View logs