small refactoring get_revnum request

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 4.54545% with 21 lines in your changes are missing coverage. Please review.

Project coverage is 58.44%. Comparing base (aa2e190) to head (79523e5).

Files	Patch %	Lines
oda_api/gallery_api.py	4.54%	21 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #246 +/- ## ========================================== + Coverage 58.25% 58.44% +0.18% ========================================== Files 23 23 Lines 4851 4849 -2 ========================================== + Hits 2826 2834 +8 + Misses 2025 2015 -10 ```

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