More accurately check that a row of text ends with a single space

[MyreMylar]

Small fix, as title.

[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 95.86%. Comparing base (65cfadf) to head (b76e1a1).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
pygame_gui/core/text/text_box_layout_row.py	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #635      +/-   ##
==========================================
- Coverage   95.87%   95.86%   -0.01%     
==========================================
  Files          90       90              
  Lines       14006    14011       +5     
==========================================
+ Hits        13428    13432       +4     
- Misses        578      579       +1     

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