Fix URL previews
Fix URL previews

and also things like the unsent message error and encryption
warning.

Stuff that we need to do at room view mount time had got moved into
a clause of the if statement in onHaveRoom and so wasn't being
executed.

Fixes https://github.com/vector-im/riot-web/issues/4327

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