Merge #5126: fix(playlist): always call onCompletion when moving media sources

Imported from GitHub PR https://github.com/google/ExoPlayer/pull/5126

Closes #5125
Merge 55a4c1e15de7f100f37e38119f1da360910fd1e3 into fe41f17c

PiperOrigin-RevId: 222612873

library/core/src/main/java/com/google/android/exoplayer2/source/ConcatenatingMediaSource.java

@@ -365,6 +365,9 @@ public class ConcatenatingMediaSource extends CompositeMediaSource<MediaSourceHo
   public final synchronized void moveMediaSource(
   public final synchronized void moveMediaSource(
       int currentIndex, int newIndex, @Nullable Runnable actionOnCompletion) {
       int currentIndex, int newIndex, @Nullable Runnable actionOnCompletion) {
     if (currentIndex == newIndex) {
     if (currentIndex == newIndex) {
+      if (actionOnCompletion != null) {
+        actionOnCompletion.run();
+      }
       return;
       return;
     }
     }
     mediaSourcesPublic.add(newIndex, mediaSourcesPublic.remove(currentIndex));
     mediaSourcesPublic.add(newIndex, mediaSourcesPublic.remove(currentIndex));