Fix G602 analyzer panic that kills gosec process

[ravisastryk]

Fixes #1489 - Running gosec with G602 enabled crashes on certain codebases.

The issue is that the G602 slice-bounds analyzer panics on certain SSA instruction patterns (nil const values, short type strings, nil blocks). Since there is no recover() in the analyzer's run path, the panic propagates and terminates the entire gosec process before any results are written.

Fix:

• Add defer recover() to the analyzer run function - G602 panic degrades to a logged error instead of crashing the process
• Nil-check handling with defensive programming strategy
• Improve code coverage

[ravisastryk]

This PR should follow after the merge of #1492

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 55.00000% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.47%. Comparing base (1216c9b) to head (92b6cb9).
⚠️ Report is 178 commits behind head on master.

Files with missing lines	Patch %	Lines
analyzers/slice_bounds.go	55.00%	5 Missing and 4 partials ⚠️
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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1491      +/-   ##
==========================================
+ Coverage   68.49%   69.47%   +0.97%     
==========================================
  Files          75       85      +10     
  Lines        4384     6748    +2364     
==========================================
+ Hits         3003     4688    +1685     
- Misses       1233     1828     +595     
- Partials      148      232      +84     

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