[SDL] SDL_mixer 1.28 never closes files opened for OGG music playback

[Ryan C. Gordon]

> SDL_mixer 1.28 never closes files opened for OGG music playback. The files get
> opened locally and then abandoned.

Mix_FreeMusic() calls OGG_delete(), which calls 
vorbis.ov_clear(&music->vf), which calls our callback function 
sdl_close_func().

At least, that's how it appears to work with the source in Subversion. 
Is my analysis accurate?

--ryan.