[Coco] DriveWire with filesizes not divisible by 256

[CoCoList for Color Computer Enthusiasts]

A couple survey responses have indicted a desire to use files of arbitrary
size in DriveWire.

Since we only read/write 256 byte sized sectors, what is the correct way to
do that?  Just fill the last sector with 0?  There isn't a way for the
server to tell the coco what's part of the file and what's not in the last
sector, and vice versa the file would become padded to 256 byte boundary if
the last sector is written, since coco can't tell server the same.  Does
that matter?  It feels a bit dangerous.

-aaron