rtmp server: fix responses to ping requests

[aler9]

No description provided.

[codecov-commenter]

Codecov Report

Merging #1245 (07c9b25) into main (8bee4af) will increase coverage by 0.25%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1245      +/-   ##
==========================================
+ Coverage   67.21%   67.47%   +0.25%     
==========================================
  Files         107      107              
  Lines        8941     8941              
==========================================
+ Hits         6010     6033      +23     
+ Misses       2363     2338      -25     
- Partials      568      570       +2     

Impacted Files	Coverage Δ
internal/rtmp/message/readwriter.go	70.83% <100.00%> (+70.83%)	⬆️
internal/core/rtmp_source.go	68.42% <0.00%> (-0.88%)	⬇️
internal/core/hls_server.go	75.74% <0.00%> (-0.50%)	⬇️
internal/core/path.go	73.28% <0.00%> (+0.38%)	⬆️
internal/core/source_static.go	70.73% <0.00%> (+3.25%)	⬆️
internal/rtmp/message/writer.go	66.66% <0.00%> (+11.11%)	⬆️

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