message: Use a ternary operator instead of relying on AND semantics in EditHIstoryDialog
  Fixes (probably).
  `allEvents` should never have a boolean in it, so given the stack trace and the code this is my best estimate for what the problem could be. I can't reproduce the problem.
diff: @@ -116,7 +116,7 @@ export default class MessageEditHistoryDialog extends React.PureComponent {
  nodes.push((
  <EditHistoryMessage
  key={e.getId()}
  - previousEdit={!isBaseEvent && allEvents[i + 1]}
  + previousEdit={!isBaseEvent ? allEvents[i + 1] : null}
  isBaseEvent={isBaseEvent}
  mxEvent={e}
  isTwelveHour={this.state.isTwelveHour}
  