[4.5] fix: send participation reply on fresh event

[phil-davis]

Backport #743 to 4.5 branch

[codecov]

Codecov Report

❌ Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 98.64%. Comparing base (365a526) to head (c990e14).
⚠️ Report is 5 commits behind head on 4.5.

Files with missing lines	Patch %	Lines
lib/ITip/Broker.php	85.71%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                4.5     #748      +/-   ##
============================================
- Coverage     98.66%   98.64%   -0.02%     
- Complexity     1935     1938       +3     
============================================
  Files            71       71              
  Lines          5301     5305       +4     
============================================
+ Hits           5230     5233       +3     
- Misses           71       72       +1     

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