[Coco] Large file deletion fails on NitrOS9/6309

[Jeff Teunissen]

Deleting files that cross a $x000 cluster boundary seems to be broken in
the latest NitrOS9, and probably has been for a very long time.

I have an uncompressed .ar file, 'cococ.ar', that's about 3 megabytes in
size. I use it to move up-to-date C source code from my Linux system to my
virtual CoCo hard disks. When I delete the archive from the disk, the
system mostly locks up -- that is, the "delete" command never finishes and
no programs can be run, though things like CLEAR to change windows still
function normally.

When I issue the command "del cococ.ar", the directory entry is marked
deleted as expected, and the allocation map is updated...but it seems to
stop updating the disk allocation map at the next $x000 cluster boundary.

On the disk, the file starts at cluster $189C and goes all the way to
cluster $5A80, and is referenced in LSNs 4-12. The deletion succeeds up to
the end of LSN 4, which describes clusters $1800-$1FFF, and then nothing
further works.