Wire local room logic (#9078)

* Wire local room logic

* Migrate to testling-lib; update test descriptions

src/Avatar.ts

@@ -22,6 +22,7 @@ import { split } from "lodash";
 
 import DMRoomMap from './utils/DMRoomMap';
 import { mediaFromMxc } from "./customisations/Media";
+import { isLocalRoom } from "./utils/localRoom/isLocalRoom";
 
 // Not to be used for BaseAvatar urls as that has similar default avatar fallback already
 export function avatarUrlForMember(
@@ -142,7 +143,12 @@ export function avatarUrlForRoom(room: Room, width: number, height: number, resi
     if (room.isSpaceRoom()) return null;
 
     // If the room is not a DM don't fallback to a member avatar
-    if (!DMRoomMap.shared().getUserIdForRoomId(room.roomId)) return null;
+    if (
+        !DMRoomMap.shared().getUserIdForRoomId(room.roomId)
+        && !(isLocalRoom(room))
+    ) {
+        return null;
+    }
 
     // If there are only two members in the DM use the avatar of the other member
     const otherMember = room.getAvatarFallbackMember();