Stop fetching room history on error
It happens easily in a room that was left, where we get the following message in a loop:
fractal::session::room::timeline: Couldn't load previous events for room the server returned an error: [403 / M_FORBIDDEN] User @######:matrix.org not in room !##########:matrix.org, and room previews are disabled: !#########:matrix.org
This error is final so we should never try to get the history again and show a message in the timeline. Errors that can be recovered from should probably show a Retry
button in the timeline.