fix: Fix accidental raise on shape 1

[ritchie46]

fixes #18736

[codecov]

Codecov Report

Attention: Patch coverage is 28.57143% with 5 lines in your changes missing coverage. Please review.

Project coverage is 79.85%. Comparing base (962b576) to head (1f6b9ed).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-core/src/frame/mod.rs	0.00%	4 Missing ⚠️
crates/polars-mem-engine/src/executors/stack.rs	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #18748      +/-   ##
==========================================
- Coverage   79.86%   79.85%   -0.01%     
==========================================
  Files        1517     1517              
  Lines      205542   205530      -12     
  Branches     2892     2892              
==========================================
- Hits       164156   164134      -22     
- Misses      40838    40848      +10     
  Partials      548      548              

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