deps/media-playback: Fix invalid seek at reset

When AVFormatContext->startime is set to AV_NO_PTS
mp_media_reset try to seek to INT64_MIN
use 0 instead.
Fix loop with aac file
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Internal Server Error - Gitea: Git with a cup of tea
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Gitea Version: 1.28.0+dev-477-g8b6ad49a5f