data_types: improve BranchName.HasRevision
data_types: improve BranchName.HasRevision

Issue: KBFS-3204

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