[FIX] Room creation error due absence of subscriptions (#11178)

Fixes the following error:

```
Uncaught TypeError: Cannot read property 'name' of undefined
    at roomList.js:127
    at callbacks.js:97
    at Array.reduce (<anonymous>)
    at Object.RocketChat.callbacks.run (callbacks.js:88)
    at Streamer.<anonymous> (cachedCollection.js:340)
    at ev.js:11
    at Array.forEach (<anonymous>)
    at Streamer.emit (ev.js:11)
    at StreamerCentral.<anonymous> (client.js:66)
    at ev.js:11
```

packages/rocketchat-ui-sidenav/client/roomList.js

@@ -124,6 +124,9 @@ const mergeSubRoom = (record/*, t*/) => {
 
 RocketChat.callbacks.add('cachedCollection-received-rooms', (room) => {
 	const sub = RocketChat.models.Subscriptions.findOne({ rid: room._id });
+	if (!sub) {
+		return;
+	}
 	const $set = {lastMessage : room.lastMessage, lm: room._updatedAt, ...getLowerCaseNames(room, sub.name)};
 	RocketChat.models.Subscriptions.update({ rid: room._id }, {$set});
 });