Make the is-alone check use efficient methods

src/components/structures/RoomView.js

@@ -729,8 +729,8 @@ module.exports = React.createClass({
             return;
         }
 
-        const joinedMembers = room.currentState.getMembers().filter((m) => m.membership === "join" || m.membership === "invite");
+        const joinedOrInvitedMemberCount = room.getJoinedMemberCount() + room.getInvitedMemberCount();
-        this.setState({isAlone: joinedMembers.length === 1});
+        this.setState({isAlone: joinedOrInvitedMemberCount === 1});
     },
 
     _updateConfCallNotification: function() {