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## Summary of the Pull Request
Uses the verification in `at` to ensure the index is correct (as @j4james suggests). If `at` throws, then returns false.
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## References
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## PR Checklist
* [x] Closes#3720
* [x] CLA signed. If not, go over [here](https://cla.opensource.microsoft.com/microsoft/Terminal) and sign the CLA
* [ ] Tests added/passed
* [ ] Requires documentation to be updated
* [x] ~~I've~~ discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #3720
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## Detailed Description of the Pull Request / Additional comments
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## Validation Steps Performed
Can no longer repro the issue after the fix.
19babc0ec5