don't assume roomKeys is an array

src/matrix/DeviceMessageHandler.js

@@ -60,12 +60,14 @@ export class DeviceMessageHandler {
     }
 
     _applyDecryptChanges(rooms, {roomKeys}) {
+        if (roomKeys && roomKeys.length) {
             const roomKeysByRoom = groupBy(roomKeys, s => s.roomId);
             for (const [roomId, roomKeys] of roomKeysByRoom) {
                 const room = rooms.get(roomId);
                 room?.notifyRoomKeys(roomKeys);
             }
         }
+    }
 
     // not safe to call multiple times without awaiting first call
     async decryptPending(rooms) {