Guard against invalid or missing URLs

[benbalter]

Fixes #198.

[DirtyF]

I tested with an invalid path for page.image with image: .\wrong\path

There's no warning on the console, the wrong path is included in the generated page metadata :

<meta property="og:image" content="http://localhost:4000/.%5Cwrong%5Cpath" />

{"@context":"http://schema.org","@type":"BlogPosting","headline":"Welcome to Jekyll!","image":"http://localhost:4000/.%5Cwrong%5Cpath","…

[benbalter]

@DirtyF what would you expect the behavior to be? My intention here was to prevent the build from failing due to invalid or missing URLs. If a user provides an invalid URL right now, we output it to the best of our ability, even if it's wrong (or isn't live, etc.).

[DirtyF]

@benbalter OK then it's fine, you're right people are responsible for what they enter and can rely on tools like html-proofer and CI to prevent invalid paths.

[DirtyF]

👍 Image Invalid path does not prevent the site from buidling.