ftp: Return the correct error code for a failed move operation
ftp: Return the correct error code for a failed move operation

When the source file does not exist for a move operation, return
G_IO_ERROR_NOT_FOUND (as specified by the docs) instead of
G_IO_ERROR_FAILED.

https://bugzilla.gnome.org/show_bug.cgi?id=710321

gicmo/gvfs,gicmo/gvfs,gicmo/gvfs,gicmo/gvfs