smbd/smb2_ioctl: fail zero length copy chunk requests

smbd/smb2_ioctl: fail zero length copy chunk requests

As documented in MS-SMB2 3.3.5.15.6 Handling a Server-Side Data Copy
Request, an invalid parameter response should be sent when:

The Length value in a single chunk is greater than
ServerSideCopyMaxChunkSize or *equal to zero*.

We do not currently abide by the latter part of this clause.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=10424

Signed-off-by: David Disseldorp <ddiss@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>