message: Fix reaction event crashes in message previews
  Fixes
diff: @@ -22,8 +22,11 @@ import { _t } from "../../../languageHandler";
  export class ReactionEventPreview implements IPreview {
  public getTextFor(event: MatrixEvent, tagId?: TagID): string {
  - const reaction = event.getRelation().key;
  - if (!reaction) return;
  + const relation = event.getRelation();
  + if (!relation) return null; // invalid reaction (probably redacted)
  +
  + const reaction = relation.key;
  + if (!reaction) return null; // invalid reaction (unknown format)
  if (isSelf(event) || !shouldPrefixMessagesIn(event.getRoomId(), tagId)) {
  return reaction;
  