Fix skin result extraction based on list of elements

[PProfizi]

Closes #423

Fixes the initial issue while adding a new request argument for mesh reduction reduce_mesh to handle the behavior expected for remote post-processing:

• [ ] add tests
• [ ] confirm design and propagate to all result requests
• [ ] add example

[codecov[bot]]

Codecov Report

Attention: 32 lines in your changes are missing coverage. Please review.

Comparison is base (d4c10ab) 83.82% compared to head (2d37b76) 83.45%. Report is 9 commits behind head on master.

:exclamation: Current head 2d37b76 differs from pull request most recent head e5abaad. Consider uploading reports for the commit e5abaad to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #532 +/- ## ========================================== - Coverage 83.82% 83.45% -0.37% ========================================== Files 47 47 Lines 5068 5120 +52 ========================================== + Hits 4248 4273 +25 - Misses 820 847 +27 ```