font: remove misleading no-op code
font: remove misleading no-op code

ass_font_get_index is _always_ called with *face_index == 0,
and even then it's only a fallback default rather than a request:
it should be treated as an output-only parameter.

astiob/libass,libass/libass,xbmc/libass,MrSmile/libass,libass/libass,ShiftMediaProject/libass,MrSmile/libass,ShiftMediaProject/libass,xbmc/libass,astiob/libass