More @nullable in SimpleDecoderAudioRenderer

Some members are nullable but were not marked as
such.

PiperOrigin-RevId: 288873481

library/core/src/main/java/com/google/android/exoplayer2/audio/SimpleDecoderAudioRenderer.java

@@ -101,10 +101,14 @@ public abstract class SimpleDecoderAudioRenderer extends BaseRenderer implements
   private Format inputFormat;
   private Format inputFormat;
   private int encoderDelay;
   private int encoderDelay;
   private int encoderPadding;
   private int encoderPadding;
-  private SimpleDecoder<DecoderInputBuffer, ? extends SimpleOutputBuffer,
-        ? extends AudioDecoderException> decoder;
-  private DecoderInputBuffer inputBuffer;
-  private SimpleOutputBuffer outputBuffer;
+
+  @Nullable
+  private SimpleDecoder<
+          DecoderInputBuffer, ? extends SimpleOutputBuffer, ? extends AudioDecoderException>
+      decoder;
+
+  @Nullable private DecoderInputBuffer inputBuffer;
+  @Nullable private SimpleOutputBuffer outputBuffer;
   @Nullable private DrmSession<ExoMediaCrypto> decoderDrmSession;
   @Nullable private DrmSession<ExoMediaCrypto> decoderDrmSession;
   @Nullable private DrmSession<ExoMediaCrypto> sourceDrmSession;
   @Nullable private DrmSession<ExoMediaCrypto> sourceDrmSession;