add try and except around blending

[peterdudfield]

Pull Request

Description

Add try and except around blending. This means national will still get saved, even if gsps are failing.

Fixes #23

How Has This Been Tested?

• CI tests

• added a test

• [ ] Yes

Checklist:

• [x] My code follows OCF's coding style guidelines
• [x] I have performed a self-review of my own code
• [ ] I have made corresponding changes to the documentation
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] I have checked my code and corrected any misspellings

[codecov[bot]]

Codecov Report

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

Comparison is base (4f63d5c) 96.44% compared to head (7b6c6f4) 97.66%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #24 +/- ## ========================================== + Coverage 96.44% 97.66% +1.21% ========================================== Files 4 4 Lines 338 342 +4 ========================================== + Hits 326 334 +8 + Misses 12 8 -4 ```

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