fix `decode_entry` on special files

fix `decode_entry` on special files

When using the random accessor to access FIFOs or sockets,
the ranged reader limits the data to only that entry, and
the `decode_entry` will never see a `PAYLOAD` or
`GOODBYE_TABLE` item to finish the entry.
Instead, it'll reach EOF and we need to handle this.
The accessor now tells the decoder to expect EOF as a valid
condition for ending the entry.

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>