Looks like a bunch of off-by-one errors.
The track number was mistakenly offset by 1 - this shifted all chapters
by one, and make the first chapter start on the second track (so the
"chapter" property returned -1 in the first track since it was before
the first chapter).
Also, the calculation of the sector destination was messed up. This
comes from commit 32d818f0, where I apparently attempted to calculate
the position to one byte before the section, but unfortunately math
doesn't work this way and it was nonsense. Just drop this idea; while it
may help with seeking (probably...), it also returns slightly different
times. The user shall use hr-seeks if accurate seeking is required.
Hopefully fixes#1560.
5bce4664be