folder_branch_ops: fix `keybase fs history` after re-login
folder_branch_ops: fix `keybase fs history` after re-login

Need to reinitialize the sync.Once object when the edit history is
cleared on logout, so chat monitoring can be started up again after
login.

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