Fix crash when there's no input player view.

This happens when the input is an image. The output will always be video so the
outputPlayer and outputVideoTextView will always present.

PiperOrigin-RevId: 524329436

demos/transformer/src/main/java/com/google/android/exoplayer2/transformerdemo/TransformerActivity.java

@@ -689,7 +689,6 @@ public final class TransformerActivity extends AppCompatActivity {
     ExoPlayer outputPlayer = new ExoPlayer.Builder(/* context= */ this).build();
     outputPlayerView.setPlayer(outputPlayer);
     outputPlayerView.setControllerAutoShow(false);
-    outputPlayerView.setOnClickListener(this::onClickingPlayerView);
     outputPlayer.setMediaItem(outputMediaItem);
     outputPlayer.prepare();
     this.outputPlayer = outputPlayer;
@@ -717,6 +716,7 @@ public final class TransformerActivity extends AppCompatActivity {
       inputPlayerView.setPlayer(inputPlayer);
       inputPlayerView.setControllerAutoShow(false);
       inputPlayerView.setOnClickListener(this::onClickingPlayerView);
+      outputPlayerView.setOnClickListener(this::onClickingPlayerView);
       inputPlayer.setMediaItem(inputMediaItem);
       inputPlayer.prepare();
       this.inputPlayer = inputPlayer;
@@ -731,13 +731,17 @@ public final class TransformerActivity extends AppCompatActivity {
 
   private void onClickingPlayerView(View view) {
     if (view == inputPlayerView) {
-      checkNotNull(inputPlayer).setVolume(1f);
-      checkNotNull(inputTextView).setText(R.string.input_video_playing_sound);
+      if (inputPlayer != null && inputTextView != null) {
+        inputPlayer.setVolume(1f);
+        inputTextView.setText(R.string.input_video_playing_sound);
+      }
       checkNotNull(outputPlayer).setVolume(0f);
       checkNotNull(outputVideoTextView).setText(R.string.output_video_no_sound);
     } else {
-      checkNotNull(inputPlayer).setVolume(0f);
-      checkNotNull(inputTextView).setText(getString(R.string.input_video_no_sound));
+      if (inputPlayer != null && inputTextView != null) {
+        inputPlayer.setVolume(0f);
+        inputTextView.setText(getString(R.string.input_video_no_sound));
+      }
       checkNotNull(outputPlayer).setVolume(1f);
       checkNotNull(outputVideoTextView).setText(R.string.output_video_playing_sound);
     }