fix: exception if on early adError (#4362)

If onAdError is called before onAdStart_ then onAdComplete_ uses
this.ad_ which is undefined.

This can happen if a VAST XML file contains no ads.

Fixes #4004

AUTHORS

@@ -43,6 +43,7 @@ Johan Sundström <[email protected]>
 Jonas Birmé <[email protected]>
 Jozef Chúťka <[email protected]>
 Jun Hong Chong <[email protected]>
+Jürgen Kartnaller <[email protected]>
 JW Player <*@jwplayer.com>
 Lucas Gabriel Sánchez <[email protected]>
 Matthias Van Parijs <[email protected]>

CONTRIBUTORS

@@ -69,6 +69,7 @@ Jonas Birmé <[email protected]>
 Jono Ward <[email protected]>
 Jozef Chúťka <[email protected]>
 Jun Hong Chong <[email protected]>
+Jürgen Kartnaller <[email protected]>
 Leandro Ribeiro Moreira <[email protected]>
 Lucas Gabriel Sánchez <[email protected]>
 Matias Russitto <[email protected]>

lib/ads/client_side_ad_manager.js

@@ -427,7 +427,7 @@ shaka.ads.ClientSideAdManager = class {
   onAdComplete_(e) {
     this.onEvent_(new shaka.util.FakeEvent(shaka.ads.AdManager.AD_STOPPED,
         (new Map()).set('originalEvent', e)));
-    if (this.ad_.isLinear()) {
+    if (this.ad_ && this.ad_.isLinear()) {
       this.adContainer_.removeAttribute('ad-active');
       this.video_.play();
     }