file-transfer-channel: Fix file transfer on windows.
file-transfer-channel: Fix file transfer on windows.

Fix file-transfer-channel so that it handles file transfers
on windows, The current code is designed not to support file
transfers on windows.

Reviewed-by: Olli Salli <20a519b27baa022954fba30203936bb6e51a67dc@collabora.co.uk>

freedesktop-unofficial-mirror/telepathy__telepathy-salut,freedesktop-unofficial-mirror/telepathy__telepathy-salut,freedesktop-unofficial-mirror/telepathy__telepathy-salut,freedesktop-unofficial-mirror/telepathy__telepathy-salut