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## Summary of the Pull Request
Fixed the noexcept specifier on `GetGuid`, and corrected `FindProfile` and `FindGuid` so they don't throw. Also, adjusted `SettingsTests` to reflect these changes.
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## References
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## PR Checklist
* [x] Closes#3763
* [x] CLA signed. If not, go over [here](https://cla.opensource.microsoft.com/microsoft/Terminal) and sign the CLA
* [x] Tests added/passed updated a test group in `SettingsTests`
* [ ] 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: #3763
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## Detailed Description of the Pull Request / Additional comments
The `noexcept` specifier on `GetGuid` was not removed when `Profile` was [updated](https://github.com/microsoft/terminal/issues/3763#issuecomment-559497094) to `std::optional<GUID>`. This PR fixes that and modifies two helper functions `FindProfile` and `FindGuid` in `CascadiaSettings` to work correctly if `GetGuid` does throw.
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## Validation Steps Performed
Updated the `TestHelperFunctions` test group in `SettingsTests` and made sure the tests pass.
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