Check if the message panel is at the end of the timeline on init
Check if the message panel is at the end of the timeline on init

Fixes https://github.com/vector-im/riot-web/issues/8503

componentDidUpdate is called a lot, and we don't really want to keep checking the messagePanel, so this introduces a new flag to check if the init is even needed.
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