Fix window index comparison.

To check the validity of a window index it needs to be compared with a greater
or equal sign to the window count.

Issue:#4822

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=213234403

RELEASENOTES.md

@@ -133,6 +133,8 @@
   ([#4774](https://github.com/google/ExoPlayer/issues/4774)).
 * Fix issue with audio discontinuities at period transitions, e.g. when
   looping ([#3829](https://github.com/google/ExoPlayer/issues/3829)).
+* Fix issue where `player.getCurrentTag()` throws an `IndexOutOfBoundsException`
+  ([#4822](https://github.com/google/ExoPlayer/issues/4822)).
 * IMA extension:
   * Refine the previous fix for empty ad groups to avoid discarding ad breaks
     unnecessarily ([#4030](https://github.com/google/ExoPlayer/issues/4030)),

extensions/cast/src/main/java/com/google/android/exoplayer2/ext/cast/CastPlayer.java

@@ -495,7 +495,7 @@ public final class CastPlayer implements Player {
   @Override
   public @Nullable Object getCurrentTag() {
     int windowIndex = getCurrentWindowIndex();
-    return windowIndex > currentTimeline.getWindowCount()
+    return windowIndex >= currentTimeline.getWindowCount()
         ? null
         : currentTimeline.getWindow(windowIndex, window, /* setTag= */ true).tag;
   }

library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerImpl.java

@@ -380,7 +380,7 @@ import java.util.concurrent.CopyOnWriteArraySet;
   @Override
   public @Nullable Object getCurrentTag() {
     int windowIndex = getCurrentWindowIndex();
-    return windowIndex > playbackInfo.timeline.getWindowCount()
+    return windowIndex >= playbackInfo.timeline.getWindowCount()
         ? null
         : playbackInfo.timeline.getWindow(windowIndex, window, /* setTag= */ true).tag;
   }