add a quick sanity check for kbfs mount default on Windows (#11482)
add a quick sanity check for kbfs mount default on Windows (#11482)

* Add a sanity test for empty default mount dir on Windows

* format

keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client