OSFS.unsyspath: work correctly for root of drive

fs/osfs/__init__.py

@@ -163,6 +163,8 @@ class OSFS(OSFSXAttrMixin, OSFSWatchMixin, FS):
         """
         path = os.path.normpath(os.path.abspath(path))
         path = self._decode_path(path)
+        if len(path) == 6 and not path.endswith("\\"):
+            path = path + "\\"
         prefix = os.path.normcase(self.root_path)
         if not prefix.endswith(os.path.sep):
             prefix += os.path.sep