Check if codec still exists before handling tunneling events

The tunneling callbacks are sent via Handler messages and may be
handled after the codec/surface was changed or released.

We already guard against the codec/surface change condition by
creating a new listener and verifying that the current callback
happens for the correct listener instance, but we don't guard
against a released codec yet.

PiperOrigin-RevId: 495882353
(cherry picked from commit 5e23b8bf)

library/core/src/main/java/com/google/android/exoplayer2/video/MediaCodecVideoRenderer.java

@@ -2047,7 +2047,7 @@ public class MediaCodecVideoRenderer extends MediaCodecRenderer {
     }
 
     private void handleFrameRendered(long presentationTimeUs) {
-      if (this != tunnelingOnFrameRenderedListener) {
+      if (this != tunnelingOnFrameRenderedListener || getCodec() == null) {
         // Stale event.
         return;
       }