fix: Fix align_frames with single row panicking

[lukemanley]

closes #20445

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 58.69%. Comparing base (0c290d6) to head (6d7f28f).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...s/polars-ops/src/frame/join/dispatch_left_right.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main   #20466       +/-   ##
===========================================
- Coverage   78.98%   58.69%   -20.29%     
===========================================
  Files        1563     1563               
  Lines      220557   220555        -2     
  Branches     2488     2488               
===========================================
- Hits       174209   129463    -44746     
- Misses      45775    90519    +44744     
  Partials      573      573               

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