fix(download): should not error when the model to be removed not existed

[zwpaper]

after fix:

before:

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 20 lines in your changes missing coverage. Please review.

Project coverage is 63.60%. Comparing base (096dd20) to head (d2f4c58).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/tabby-download/src/lib.rs	0.00%	20 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3296      +/-   ##
==========================================
- Coverage   63.63%   63.60%   -0.04%     
==========================================
  Files         187      187              
  Lines       20813    20820       +7     
==========================================
- Hits        13245    13243       -2     
- Misses       7568     7577       +9     

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