Ensure AS users are registered before processing membership events

Author: sandhose

src/appservice/Appservice.ts

@@ -635,6 +635,7 @@ export class Appservice extends EventEmitter {
 
         // Update the target intent's joined rooms (fixes transition errors with the cache, like join->kick->join)
         const intent = this.getIntentForUserId(event['state_key']);
+        await intent.ensureRegistered();
         await intent.refreshJoinedRooms();
 
         const targetMembership = event["content"]["membership"];