record, hls: fix panic with MPEG-4 audio tracks without config (#3590)

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[codecov]

Codecov Report

Attention: Patch coverage is 62.67606% with 53 lines in your changes missing coverage. Please review.

Please upload report for BASE (main@da5420a). Learn more about missing BASE report.

Files	Patch %	Lines
internal/servers/hls/muxer_instance.go	0.00%	21 Missing ⚠️
internal/record/format_fmp4.go	60.97%	12 Missing and 4 partials ⚠️
internal/record/format_mpegts.go	65.62%	8 Missing and 3 partials ⚠️
internal/protocols/mpegts/from_stream.go	0.00%	5 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3594   +/-   ##
=======================================
  Coverage        ?   57.07%           
=======================================
  Files           ?      190           
  Lines           ?    19176           
  Branches        ?        0           
=======================================
  Hits            ?    10944           
  Misses          ?     7402           
  Partials        ?      830           

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[github-actions]

This issue is mentioned in release v1.8.5 🚀
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