fix: Return correct value for when().then().else() on structs when using first()\last()

[barak1412]

Fixes #18961.

[ritchie46]

Nice, can you add a test?

[barak1412]

@ritchie46

When this PR will be merged, #18930 will fix assert_frame_equal, and the existing test will verify it.
Do you want me to add a separate test?

[ritchie46]

Do you want me to add a separate test?

Yes, that won't hurt. :)

[barak1412]

@ritchie46

Sure! I will try get to it afternoon, if not - on sunday.
Thanks.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.86%. Comparing base (71a8b05) to head (54e87a5).
Report is 21 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #18969      +/-   ##
==========================================
- Coverage   79.88%   79.86%   -0.02%     
==========================================
  Files        1522     1523       +1     
  Lines      206958   207504     +546     
  Branches     2906     2904       -2     
==========================================
+ Hits       165322   165724     +402     
- Misses      41088    41233     +145     
+ Partials      548      547       -1     

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[barak1412]

@ritchie46 Added test.

[ritchie46]

Thank you @barak1412