message: Don't group blank membership changes
  We already drop noop membership changes when they don't make it into a MELS, so we just need to make the MELS aware enough to drop messages early that are noops.
  Fixes
diff: @@ -962,6 +962,17 @@ class MemberGrouper {
  }
  add(ev) {
  + if (ev.getType() === 'm.room.member') {
  + // We'll just double check that it's worth our time to do so...
  + if (ev.getPrevContent()) {
  + const membershipChange = ev.getPrevContent()['membership'] !== ev.getContent()['membership'];
  + const displayNameChange = ev.getPrevContent()['displayname'] !== ev.getContent()['displayname'];
  + const avatarChange = ev.getPrevContent()['avatar_url'] !== ev.getContent()['avatar_url'];
  + if (!membershipChange && !displayNameChange && !avatarChange) {
  + return; // Not a substantial change - quietly ignore
  + }
  + }
  + }
  this.readMarker = this.readMarker || this.panel._readMarkerForEvent(ev.getId());
  this.events.push(ev);
  }
  