Quell static-analysis concern about div-by-0

[justsmth]

Issues:

Addresses #1856

Description of changes:

Clarify pkcs8 logic so it doesn't trip up static analysis.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.46%. Comparing base (7090b90) to head (8705354).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1866      +/-   ##
==========================================
- Coverage   78.46%   78.46%   -0.01%     
==========================================
  Files         585      585              
  Lines       99457    99458       +1     
  Branches    14236    14238       +2     
==========================================
- Hits        78038    78035       -3     
- Misses      20784    20787       +3     
- Partials      635      636       +1     

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