tools/obexctl: Fix display of size on completion

Outputs zero as the transferred size on completion of transfer as below:

  [CHG] Transfer /org/bluez/obex/server/session3/transfer2 Transferred: 5339965 (@32KB/s 00:01)
  [CHG] Transfer /org/bluez/obex/server/session3/transfer2 Transferred: 5372726 (@32KB/s 00:00)
  [CHG] Transfer /org/bluez/obex/server/session3/transfer2 Transferred: 0 (@18446744073704178KB/s 00:00)
  [CHG] Transfer /org/bluez/obex/server/session3/transfer2 Status: complete
1 file changed