oggz uses reverse calculation for vorbis granulepos when forward calculation would work
When using liboggz with the OGGZ_AUTO option to reconstruct missing granulepos entries, reconstruction for Vorbis audio packets is always done using the reverse calculation from the last packet in a page, and never in the forwards direction.
The forward calculation was disabled in this 2007 commit:
by adding an early 'return -1' into auto_calc_vorbis.
I'm not sure if it was supposed to do that (why keep the unreachable code?) or if that was a test for debugging that got committed by mistake.
If I manually remove the 'return -1', the forward reconstruction happens one packet at a time as I expect it, but I don't know if there's anything else wrong with that formerly-unreachable code.