What is the purpose of this pull request?

• Documentation update
• Bug fix
• Feature addition or enhancement
• Code maintenance
• DevOps
• Improve developer experience
• Others, please explain:

Overview of changes:
Fixes #2570

Currently, there is an issue when using the markbind serve command in non-Markbind directories, leading to an UncaughtException that is displayed to the user.

The problem seems to be due to be a missing process.exit() after catching the error. This leads to the code continuing on despite the rootFolder still being undefined.

Anything you'd like to highlight/discuss:
This PR only fixes the UncaughtException issue, not the underlying issue mentioned in #1825.

Testing instructions:
Try using the markbind serve command in a non-Markbind directory. The UncaughtException should not show. For example:

Proposed commit message: (wrap lines at 72 characters)
Catch UncaughtException when serving in non-Markbind directories

Checklist: ☑️

• Updated the documentation for feature additions and enhancements
• Added tests for bug fixes or features
• Linked all related issues
• No unrelated changes

Reviewer checklist:

Indicate the SEMVER impact of the PR:

• Major (when you make incompatible API changes)
• Minor (when you add functionality in a backward compatible manner)
• Patch (when you make backward compatible bug fixes)

At the end of the review, please label the PR with the appropriate label: r.Major, r.Minor, r.Patch.

Breaking change release note preparation (if applicable):

• To be included in the release note for any feature that is made obsolete/breaking

Give a brief explanation note about:

• what was the old feature that was made obsolete
• any replacement feature (if any), and
• how the author should modify his website to migrate from the old feature to the replacement feature (if possible).