Only install handler when first listener is registered

[Baptouuuu]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.68%. Comparing base (7edf746) to head (a24f0b9).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@              Coverage Diff              @@
##             develop       #9      +/-   ##
=============================================
+ Coverage      95.07%   95.68%   +0.60%     
- Complexity       118      119       +1     
=============================================
  Files             18       18              
  Lines            386      394       +8     
=============================================
+ Hits             367      377      +10     
+ Misses            19       17       -2     

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