Fix a bug of vfs on macos

[tygzx]

when system is macos, the pathlib.Path return was PosixPath, The PosixPath object does not have the is_relative_to method

[AeonLucid]

There is no if statement inside the try/catch, is this on purpose?

[tygzx]

I run into this problem when I run example_douyin.py....and no if statement just Is to keep the upper and lower codes consistent.

[hzyitc]

I make some changes at #70