Libass rendering uses two renderer objects to support both VSFilter
aspect ratio (mis)behavior emulation and correct rendering. When
option values were changed during playback the changes were applied to
the renderer used for the currently active track only, and old values
could be used if the user then switched to a track using the other
renderer object. Fix to update both renderers.
The --ass-force-style option was only applied when the main libass
library handle was created. Thus any per-file option changes later had
no effect. Do the ass_set_style_overrides() call in per-file
initialization instead so that possible changes will be applied. Also
move the option variable to the option struct.
Current libass will crash (usually) if you set style overrides to a
nonempty value, then an empty one. It'll be easier to trigger this bug
after this commit, but the problem is not on mplayer2 side. The fix is
trivial so hopefully there will be a fixed libass soon.