Check IS v2 account tokens for validity
Check IS v2 account tokens for validity

Fixes https://github.com/vector-im/riot-web/issues/10452

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