don't hit sig/get if we don't have to (#14107)
don't hit sig/get if we don't have to (#14107)

* don't hit sig/get if we don't have to

- the merkle tree might say our cached copy is up-to-date, and we would have been hitting the sig/get endpoint just to get a nil update, so eliminate the RT

* renames from review

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