SerialDisk 3.0 compatibility issues with EmuTOS 1.2.1

[z80andrew]

Issue desription
Copying files from Atari to PC outside of PC root folder does not work correctly when using EmuTOS.
Serial communication happens as expected but no file is written to the PC.
Copying files and folders to the Atari works as expected.

Steps to reproduce
Copy a file from the Atari to a non-root folder on the virtual disk.

Expected result
File is written to disk.

Actual result
No file is written.

Test environment 1
Atari STe / 4 MiB RAM / EmuTOS 1.2.1 floppy disk

Test environment 2
Hatari / Atari STe / 4 MiB RAM / EmuTOS 1.2.1 512K ROM