Take care of mangled paths on download as well

Take care of mangled paths on download as well

This means adjusting PropagateDownloadEncrypted so that it knows where
the file will end (otherwise it would create temporary files in non
existant paths for instance).
In turn we have to adjust PropagateDownloadFile accordingly so that it
resolves the local folder the file will end up in.
And last we adjust PropagateLocalMkdir to resolve paths as well and
demangle as needed.

Signed-off-by: Kevin Ottens <kevin.ottens@nextcloud.com>