AAC + Passthru ignores "Downmix audio to:" setting.

[W R]

Whenever I open a file with DTS or AC-3 tracks, and choose the 'AAC + Passthru' option, the AAC track created is always down mixed to 'Stereo', regardless of how I've set 'Downmix audio to:'.

[Ueli]

I just made a pull request with a fix.

[Damiano Galassi]

Fixed by Ueli in fd01fb9