#972 Audio -> stereo mode -> reverse broken on Mono input

[koko]

reverse stereo mode is broken when playing mono videos. Crashes mplayer, outputs only right ear in mvp. Pretty obscure feature. I only started using it because I made a mistake when soldering my audio extension cable and was too lasy to fix it properly :-)

mplayer:

Opening audio decoder: [ffmpeg] FFmpeg/libavcodec audio decoders
AUDIO: 44100 Hz, 1 ch, floatle, 96.0 kbit/6.80% (ratio: 12000->176400)
ID_AUDIO_BITRATE=96000
ID_AUDIO_RATE=44100
ID_AUDIO_NCH=1
Selected audio codec: [ffaac] afm: ffmpeg (FFmpeg AAC (MPEG-2/MPEG-4 Audio))
==========================================================================
[channels] Invalid routing in pair nr. 1.
[libaf] Reinitialization did not work, audio filter 'channels' returned error code -2
Error at audio filter chain pre-init!

Exiting... (Fatal error)
ID_EXIT=ERROR

Nothing interesting in mvp log, but plays only in right ear