factor out the peek rule calculation so that we can do it both onNewRoom and if there's a room already. I guess we could do it in react's onStateUpdate too

src/components/structures/RoomView.js

@@ -115,7 +115,8 @@ module.exports = React.createClass({
         // We can't try to /join because this may implicitly accept invites (!)
         // We can /peek though. If it fails then we present the join UI. If it
         // succeeds then great, show the preview (but we still may be able to /join!).
-        if (!this.state.room && this.props.autoPeek) {
+        if (!this.state.room) {
+            if (this.props.autoPeek) {
                 console.log("Attempting to peek into room %s", this.props.roomId);
                 MatrixClientPeg.get().peekInRoom(this.props.roomId).done(() => {
                     this.setState({
@@ -125,14 +126,16 @@ module.exports = React.createClass({
                     // we don't need to do anything - JS SDK will emit Room events
                     // which will update the UI. We *do* however need to know if we
                     // can join the room so we can fiddle with the UI appropriately.
-                var peekedRoom = MatrixClientPeg.get().getRoom(this.props.roomId);
-                if (!peekedRoom) {
-                    return;
-                }
+
+                    // ...XXX: or do we? can't we just do them onNewRoom?
                 }, function(err) {
                     console.error("Failed to peek into room: %s", err);
                 });
             }
+        }
+        else {
+            this._calculatePeekRules(this.state.room);
+        }
     },
 
     componentWillUnmount: function() {
@@ -284,7 +287,12 @@ module.exports = React.createClass({
             this.setState({
                 room: room
             });
+        }
 
+        this._calculatePeekRules(room);
+    },
+
+    _calculatePeekRules: function(room) {
         var guestAccessEvent = room.currentState.getStateEvents("m.room.guest_access", "");
         if (guestAccessEvent && guestAccessEvent.getContent().guest_access === "can_join") {
             this.setState({
@@ -298,7 +306,6 @@ module.exports = React.createClass({
                 canPeek: true
             });
         }
-        }
     },
 
     onRoomName: function(room) {