[Windows] ウィンドウを閉じるまでに時間がかかるのを修正

[4ster1sk]

Fix: #655
デスクトップ環境以外では_initWindow内で処理しないようにしました

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 27.68%. Comparing base (6955662) to head (baaf1a7).
Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
lib/main.dart	0.00%	3 Missing ⚠️

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Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #663      +/-   ##
===========================================
- Coverage    27.69%   27.68%   -0.01%     
===========================================
  Files          312      312              
  Lines        16253    16255       +2     
===========================================
  Hits          4501     4501              
- Misses       11752    11754       +2     

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