Catch case where new Hazard fraction is unintentionally zero

[peanutfun]

Changes proposed in this PR:

• Throw an error when selecting a part of the hazard where the fraction is zero everywhere, but only if it has had non-zero entries before.

This PR fixes #866

PR Author Checklist

• [x] Read the Contribution Guide
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• [x] Descriptive pull request title added
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• [ ] Documentation updated
• [x] Tests updated
• [x] Tests passing
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• [ ] Tests passing
• [ ] No new linter issues

[chahank]

All good, but weirdly some unit test for plotting are failing ... I have not yet understood were the failure comes from.

[chahank]

There remains an error with the compatibility with Petals, but I think this is unrelated. Good to merge!

[peanutfun]

Yes, the error is related to the centroids PRs. Will merge.

[emanuel-schmid]

Very well. Many thanks! 🙌