Fixes lastN video change. Resulting 'Uncaught TypeError: stream.getOriginalStream is not a function', problem detected by torture (3 participants and the last one receives last-n changed event on joining and screenshot shows: it is missing one of the participants and logs contain this error).

modules/UI/videolayout/VideoLayout.js

@@ -747,7 +747,7 @@ var VideoLayout = (function (my) {
                         updateLargeVideo = false;
                     }
                     remoteVideos[resourceJid].
-                        waitForPlayback(sel, mediaStream.stream);
+                        waitForPlayback(sel, mediaStream);
                 }
             });
         }