fix NPE for invites

src/RoomListSorter.js

@@ -17,8 +17,13 @@ limitations under the License.
 'use strict';
 
 function tsOfNewestEvent(room) {
+    if (room.timeline.length) {
         return room.timeline[room.timeline.length - 1].getTs();
     }
+    else {
+        return Number.MAX_SAFE_INTEGER;
+    }
+}
 
 function mostRecentActivityFirst(roomList) {
     return roomList.sort(function(a,b) {