rtmp server: fix compatibility with Neko

[aler9]

Fixes #1177

[codecov-commenter]

Codecov Report

Merging #1405 (3afd899) into main (97c1e68) will increase coverage by 0.16%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1405      +/-   ##
==========================================
+ Coverage   65.16%   65.33%   +0.16%     
==========================================
  Files         119      119              
  Lines       12889    12891       +2     
==========================================
+ Hits         8399     8422      +23     
+ Misses       3818     3794      -24     
- Partials      672      675       +3     

Impacted Files	Coverage Δ
internal/rtmp/conn.go	63.64% <100.00%> (+0.09%)	⬆️
internal/core/webrtc_conn.go	54.56% <0.00%> (-0.34%)	⬇️
internal/core/hls_muxer.go	50.94% <0.00%> (-0.24%)	⬇️
internal/hls/client_processor_fmp4.go	64.88% <0.00%> (ø)
internal/core/rtmp_source.go	67.80% <0.00%> (+2.05%)	⬆️
internal/core/path.go	73.22% <0.00%> (+2.80%)	⬆️
internal/core/source_static.go	69.92% <0.00%> (+3.00%)	⬆️

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