title: pytorch int32 to int64 conversion
body: <p>I'm trying to convert a simple image mask to <code>int64</code></p>
  <pre class="lang-py prettyprint-override"><code>image = np.array([[1, 2], [3, 4]], dtype='int32')
  
  transform = Compose([
      torch.from_numpy, 
      ConvertImageDtype(torch.int64)
  ])
  </code></pre>
  <p>However, <code>transform(image)</code> yields</p>
  <pre><code>tensor([[ 4294967296,  8589934592],
          [12884901888, 17179869184]])
  </code></pre>
  <p>Is there something wrong, or am I fundamentally misunderstanding something about how the conversion should work?</p>