Retain decoder instance after the renderer is disabled

Issue: #2826

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=216852679

library/core/src/main/java/com/google/android/exoplayer2/mediacodec/MediaCodecRenderer.java

@@ -558,6 +558,16 @@ public abstract class MediaCodecRenderer extends BaseRenderer {
 
   @Override
   protected void onDisabled() {
+    if (drmSession != null || pendingDrmSession != null) {
+      // TODO: Do something better with this case.
+      onReset();
+    } else {
+      flushOrReleaseCodec();
+    }
+  }
+
+  @Override
+  protected void onReset() {
     format = null;
     availableCodecInfos = null;
     try {