Don;t try to fetch push rules if we're a guest: it throws.

src/components/views/rooms/RoomSettings.js

@@ -37,12 +37,14 @@ module.exports = React.createClass({
         });
 
         var areNotifsMuted = false;
+        if (!MatrixClientPeg.get().isGuest()) {
             var roomPushRule = MatrixClientPeg.get().getRoomPushRule("global", this.props.room.roomId);
             if (roomPushRule) {
                 if (0 <= roomPushRule.actions.indexOf("dont_notify")) {
                     areNotifsMuted = true;
                 }
             }
+        }
 
         return {
             name: this._yankValueFromEvent("m.room.name", "name"),