fix a possible underflow on getPruningHandler

[BeniaminDrasovean]

Reasoning behind the pull request

Proposed changes

Testing procedure

Pre-requisites

Based on the Contributing Guidelines the PR author and the reviewers must check the following requirements are met:

• was the PR targeted to the correct branch?
• if this is a larger feature that probably needs more than one PR, is there a feat branch created?
• if this is a feat branch merging, do all satellite projects have a proper tag inside go.mod?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.73%. Comparing base (72468d8) to head (222d301).

Additional details and impacted files

@@                  Coverage Diff                   @@
##           feat/testnet-fixes    #7911      +/-   ##
======================================================
- Coverage               77.74%   77.73%   -0.01%     
======================================================
  Files                     887      887              
  Lines                  126451   126451              
======================================================
- Hits                    98309    98302       -7     
- Misses                  21644    21648       +4     
- Partials                 6498     6501       +3     

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