skins2: fix skins2 audio volume and adapt to latest change
- use the overall volume managed by the playlist rather than
aout_volumeGet() that now only works when a aout is running.
This is no problem since the skins2 volume slider functionally
reflects this overall volume managed by the playlist anyway.
- stick to what include/vlc_aout_intf.h lets us know about volume
boundaries(as of today, AOUT_VOLUME_DEFAULT and AOUT_VOLUME_MAX)
and infer volume to be in the [0., AOUT_VOLUME_MAX/AOUT_VOLUME_DEFAULT]
range as requested by some functions taking a float as parameter.
projects / vlc / commit