fix(screenshot): screenshot thumbnail undefined

[ycjcl868]

Close #165

[codecov]

Codecov Report

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

Project coverage is 25.46%. Comparing base (d671c7a) to head (758cb17).

Files with missing lines	Patch %	Lines
src/main/agent/operator.ts	28.57%	3 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #170      +/-   ##
==========================================
- Coverage   25.59%   25.46%   -0.14%     
==========================================
  Files          67       67              
  Lines        1516     1520       +4     
  Branches      238      240       +2     
==========================================
- Hits          388      387       -1     
- Misses       1083     1086       +3     
- Partials       45       47       +2     

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