app will crash if settings is invalid

Fixes issue described in full detail in #22

Checklist

[ ] Keep pull requests small so they can be easily reviewed.
[ ] Update the documentation, please follow the numpy style guide.
[ ] Update tests.
[ ] Categorize the PR by setting a good title and adding one of the labels: bug, feature, ui, change, documentation, breaking, ci as they show up in the changelog.
[ ] Link this PR to related issues by using closing keywords.
[ ] Add a milestone to the PR (and related issues, if any) for the intended release.
[ ] Request a review from another developer.