checkIfAlone() filters the whole member list, which is fine until we do it once for every membership event, then we have an n^2 problem. Move it into the rate limited function. Fixes https://github.com/vector-im/riot-web/issues/7163
checkIfAlone() filters the whole member list, which is fine until we do it once for every membership event, then we have an n^2 problem. Move it into the rate limited function. Fixes https://github.com/vector-im/riot-web/issues/7163