Fix vector-im/riot-web#2833 : Fail nicely when people try to register numeric user IDs
Fix vector-im/riot-web#2833 : Fail nicely when people try to register numeric user IDs

aperezdc/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,aperezdc/matrix-react-sdk,matrix-org/matrix-react-sdk,aperezdc/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,aperezdc/matrix-react-sdk