message: Fix exception when stripping replies from an event with a null body
diff: @@ -421,7 +421,7 @@ export function bodyToHtml(content: IContent, highlights: string[], opts: IOpts
  }
  let formattedBody = typeof content.formatted_body === 'string' ? content.formatted_body : null;
  - const plainBody = typeof content.body === 'string' ? content.body : null;
  + const plainBody = typeof content.body === 'string' ? content.body : "";
  if (opts.stripReplyFallback && formattedBody) formattedBody = ReplyThread.stripHTMLReply(formattedBody);
  strippedBody = opts.stripReplyFallback ? ReplyThread.stripPlainReply(plainBody) : plainBody;
  