fix: Closure compiler removes call to modifyCueCallback in src= mode (#8261)

Author: matvp91

lib/player.js

@@ -5434,7 +5434,15 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
       for (const nativeCue of nativeCues) {
         const cue = shaka.text.Utils.mapNativeCueToShakaCue(nativeCue);
         if (cue) {
-          this.config_.mediaSource.modifyCueCallback(cue, null, time);
+          const modifyCueCallback = this.config_.mediaSource.modifyCueCallback;
+          // Closure compiler removes the call to modifyCueCallback for reasons
+          // unknown to us.
+          // See https://github.com/shaka-project/shaka-player/pull/8261
+          // We'll want to revisit this condition once we migrated to TS.
+          // See https://github.com/shaka-project/shaka-player/issues/8262 for TS.
+          if (modifyCueCallback) {
+            modifyCueCallback(cue, null, time);
+          }
           allCues.push(cue);
         }
       }