folder_branch_ops: "badPtr" comments suggested by @akalin-keybase
folder_branch_ops: "badPtr" comments suggested by @akalin-keybase

Issue: #670

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