Fix false violation for unspecified namespaces

[dundalek]

When running the latest version, I noticed we introduced a regression in #30 which results in namespaces not covered in any layer (like libraries) being reported as violations.

The cause is when layer config does not contain :accessed-by-layers then due to when-let the result from dependency-layer-can-be-accessed-by-layer? will be nil, which is then negated in violate?. Same thing applies for layer-can-access-dependency-layer?.

To fix it I flipped the negation.

Checklist

• [ ] I created an issue to discuss the problem I am trying to solve or an open issue already exists.
• [x] I added a new entry to CHANGELOG.md
• [ ] I updated documentation if applicable (docs folder)

[dundalek]

This might actually still be broken when mixing both :access-layers and :accessed-by-layers.

[dundalek]

Nice catch @dundalek! I'm really enjoying our partnership.

@fabiodomingues Likewise, great to meet someone from the Clojure community with interest in this topic.