Fix a race condition handling gappy syncs
Fix a race condition handling gappy syncs

We had a problem handling gappy syncs: resetting the timeline would trigger a
pagination request (which would return no results, because there are no events
at this point); this would make the pagination requests which are spawned when
we process the events in the sync get ignored - with the result that we get a
blank window.

The fix is to avoid the ScrollPanel when we are processing new live events and
tell the TimelineWindow to paginate itself directly.

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