fix(large-video): ensure switch to local video when all others leave (#1607)

* fix(large-video): ensure switch to local video when all others leave

This handles the case where User A and B are in a call and B has
no audio or video. Then B leaves. User A would see User B left
on large video. Instead, User A should see self view on large.

* squash: always update large video if it is empty

* squash: add largeVideo check for filmstrip only mode

modules/UI/videolayout/VideoLayout.js

      * otherwise elects new video, in this order.
      */
     updateAfterThumbRemoved (id) {
-        if (!this.isCurrentlyOnLarge(id)) {
+        // Always trigger an update if large video is empty.
+        if (!largeVideo
+            || (this.getLargeVideoID() && !this.isCurrentlyOnLarge(id))) {
             return;
         }