App crashes when clicking "Optimize Geometry" without any atom

[perminder-17]

Describe the bug
When attempting to optimize geometry in the application without adding any atoms, the app crashes. This occurs specifically when navigating to Extension -> Optimize Geometry without prior addition of a molecule.

To Reproduce
Steps to reproduce the behavior:

1. Don't add any atom.
2. Go to Extension
3. Click on Optimize Geometry
4. See error

Expected behavior
The app should not crash.

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[perminder-17]

Made a PR for this @ghutchis .