[WebGL backend] Wrong results for AutoML Object model

[Linchenn]

When executing AutoML Object model with the following code snippet, it works for 3.19.0 version of WebGL backend, but it does not work for the current github repo.

const url =
          'https://storage.googleapis.com/tfjs-testing/tfjs-automl/object_detection/model.json';
const model = await tf.loadGraphModel(url);
const OUTPUT_NODE_NAMES =
          ['Postprocessor/convert_scores', 'Postprocessor/Decode/transpose_1'];
const feedDict = {ToFloat: tf.zeros([1, 224, 224, 3])};

await model.executeAsync(feedDict, OUTPUT_NODE_NAMES);