Fix config file search when stdin

[jhrmnn]

Without the fix, the search starts one directory above the current directory.

[danielhollas]

I just ran into this as well. The fix looks good to me. It would be nice to have a test for this, maybe extending / modifying this test case:

https://github.com/pseewald/fprettify/blob/cb254022c2034ad3b8f744f4dad1bf5b7438815d/fprettify/tests/init.py#L253