Revert "player: simplify audio reset when seeking"

This reverts commit 75dd3ec2106701cb865f52966de66c51cb6f9204.

This broke seeking with ordered chapters in some situations. While
the reverted commit was perfectly fine for playback of normal files,
it overlooked that in the ordered chapters case switching segments
actually reinitialized the audio chain completely, including the
decoder. And decoders still read packets on initialization. We can
restore the original commit as soon as decoders stop doing this.