fix: initialize data_source when NVD is disabled

[Mayankrai449]

fixes #3801

• Updated default_source initialization when NVD is disabled.

[codecov-commenter]

Codecov Report

Attention: 14 lines in your changes are missing coverage. Please review.

Comparison is base (d6cbe40) 75.41% compared to head (0f052bf) 80.96%.
Report is 11 commits behind head on main.

Files	Patch %	Lines
cve_bin_tool/sbom_detection.py	76.00%	4 Missing and 2 partials ⚠️
cve_bin_tool/extractor.py	64.28%	4 Missing and 1 partial ⚠️
cve_bin_tool/cli.py	78.57%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3814      +/-   ##
==========================================
+ Coverage   75.41%   80.96%   +5.55%     
==========================================
  Files         808      809       +1     
  Lines       11983    12036      +53     
  Branches     1598     1612      +14     
==========================================
+ Hits         9037     9745     +708     
+ Misses       2593     1873     -720     
- Partials      353      418      +65     

Flag	Coverage Δ
longtests	80.39% <74.19%> (+4.97%)	⬆️
win-longtests	78.78% <74.19%> (?)

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[terriko]

We should probably have some tests for this, but I'm really curious to see if it solves the issue for #3801 so I'm going to merge but also file an issue for a test.