Fix `GslibAngles` implementation

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (ef4e392) 80.89% compared to head (c7adec8) 80.93%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #193 +/- ## ========================================== + Coverage 80.89% 80.93% +0.04% ========================================== Files 21 21 Lines 382 383 +1 ========================================== + Hits 309 310 +1 Misses 73 73 ```

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