Improve path handling for Python >= 3.6

Prevents a crash when unicode strings created from non-pure utf-8 text with
'surrogateescape' error handling are used as paths for the fuse file system
(e.g. latin-1 encoded file names).

Fix accessing paths with arbitrary but allowed bytes (e.g. latin-1 encoded file names) which do not encode
utf-8 characters.

Author: seahawk1986