When the nal_unit_type of HLS is 9, it should be ignored directly.

[winlinvip]

https://github.com/winlinvip/simple-rtmp-server/issues/281

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[winlinvip]

9 is AUD, it is used to split frames.

Due to the insertion of AUD-9 during HLS writing, if not ignored, it will result in duplicate AUD-9, causing abnormalities in some players.

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