SPURIOUSZERO change

It seems that the Sanyo 7400 bombs out in the filesystem because it can have
a null filename. I don't know if this is an indication of some corruption on
the phone, or something real and legal.

The filesystem listing bombs out on this null length filename because the
com_brew.SPURIOUSZERO class gets confused, thinks there is a spurious zero
and consumes a byte.

I patched com_brew.py to not consume a byte if the two zero's (dirname len
and filename len) are the last two bytes in the buffer.

I would appreciate if other developers could test that this doesn't break
file system listing, particularly on phones with the spurious zero problem.
I tested with the Samsung A620.

Stephen