fix: correctly check for local or pre-db-update reaction via RSSI == 0

[1nv]

SNR == 0 can possibly be observed for remote messages, while RSSI == 0 (also default value) cannot.

This is a follow-up fix for #3964.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.56%. Comparing base (a4148c9) to head (5afaa9f).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #4024   +/-   ##
=====================================
  Coverage   0.56%   0.56%           
=====================================
  Files        405     405           
  Lines      24136   24136           
  Branches    3098    3098           
=====================================
  Hits         136     136           
  Misses     23979   23979           
  Partials      21      21           

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