[android] Fix leaked window in test app's BulkMarkerActivity. (#15597)

platform/android/MapboxGLAndroidSDKTestApp/src/main/java/com/mapbox/mapboxsdk/testapp/activity/annotation/BulkMarkerActivity.java

@@ -151,6 +151,9 @@ public class BulkMarkerActivity extends AppCompatActivity implements AdapterView
   @Override
   protected void onDestroy() {
     super.onDestroy();
+    if (progressDialog != null) {
+      progressDialog.dismiss();
+    }
     mapView.onDestroy();
   }