`readRaw8` throws an exception if you run out of data. This did not
turn up during my testing, because I was reading back a disk written by
fluxengine, so everything was aligned to the index pulse and no sector
ever straddled a revolution. On a "real" apple2-written disk, this was
not the case.
Incidentally, the "extra 0" problem exists on a real apple2-written
floppy as well.
It's not OK to call seek() here. Instead, add a function which can read
an apple 8-bit flux value in terms of readRaw8 and readRawBits. Apply
this function to all the data bytes, rather than just the first one.
fluxmap. This requires resetting the FluxDecoder, which loses any pending
state, resulting in bad reads for (some) formats which don't have gaps between
sectors --- the DVK MX is the main victim.
