Fix blank toast in Transformer Demo

PiperOrigin-RevId: 480847967
(cherry picked from commit 7e8f0f09)

demos/transformer/src/main/java/androidx/media3/demo/transformer/TransformerActivity.java

@@ -460,8 +460,7 @@ public final class TransformerActivity extends AppCompatActivity {
     informationTextView.setText(R.string.transformation_error);
     progressViewGroup.setVisibility(View.GONE);
     debugFrame.removeAllViews();
-    Toast.makeText(
-            TransformerActivity.this, "Transformation error: " + exception, Toast.LENGTH_LONG)
+    Toast.makeText(getApplicationContext(), "Transformation error: " + exception, Toast.LENGTH_LONG)
         .show();
     Log.e(TAG, "Transformation error", exception);
   }