fix possible panic in sig verification

[tzemanovic]

Describe your changes

The index op used to look-up signatures may fail if there isn't matching number of signatures.

Indicate on which release or other PRs this topic is based on

v0.40.0

Checklist before merging to draft

• I have added a changelog
• Git history is in acceptable state

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 53.47%. Comparing base (8479d38) to head (a8d74f0).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3543      +/-   ##
==========================================
- Coverage   53.48%   53.47%   -0.01%     
==========================================
  Files         320      320              
  Lines      110000   110001       +1     
==========================================
- Hits        58832    58825       -7     
- Misses      51168    51176       +8     

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