Commit 7484ae8e2e attempted to introduce two ass_library handles
(as it was needed to deal with how ass_library manages fonts), but the
commit was completely bogus: it assumed osd_state->ass_library would be
used by osd_libass.c only, which is not the case. As result, some of the
subtitle code used the wrong ass_library handle.
We need two ass_library handles in osd_state. The one from the mplayer
core for subtitles (osd_state->ass_library), and one for OSD rendering
(osd_state->osd_ass_library).
fb563de255