Fix reading environment variables in correct encoding

[hluk]

Fixes #3401

[codecov]

Codecov Report

❌ Patch coverage is 92.30769% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.28%. Comparing base (5c722ee) to head (43e1c54).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/app/app.cpp	87.50%	1 Missing ⚠️
src/gui/theme.cpp	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3430   +/-   ##
=======================================
  Coverage   80.28%   80.28%           
=======================================
  Files         238      238           
  Lines       29911    29903    -8     
=======================================
- Hits        24014    24008    -6     
+ Misses       5897     5895    -2     

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