Cube maps are special in that they have separate teximages for each
face. We handled that by copying the data to them separately, but in
case zoffset != 0 or depth != 6 we would read off the end of the client
array or modify the wrong images.

zoffset/depth have already been verified by the time the code gets to
this stage, so no need to double-check.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Brian Paul <brianp@vmware.com>
Cc: "10.6 11.0" <mesa-stable@lists.freedesktop.org>