title: pycuda.driver.pagelocked_empty() returns empty list
body: <p>I have retrained a model with tensorflow v2 and I want it to run on a Jetson Nano GPU. For that I had to save the model from .h5 as .pb then to .onnx and then to .trt (for which I also had to make the conversion to onnx with opset 12).</p>
  <p>Now when I can finally run the model, I am reusing an old code that used to work with the old .trt model but at locking a page:</p>
  <pre><code>import pycuda.driver as cuda
  ....
  
  
  for binding in engine:  
          size = trt.volume(engine.get_binding_shape(binding)) * engine.max_batch_size  
          dtype = trt.nptype(engine.get_binding_dtype(binding))
          host_mem = cuda.pagelocked_empty(size, dtype)
          device_mem = cuda.mem_alloc(host_mem.nbytes)
  </code></pre>
  <p>This results in an error:</p>
  <pre><code>pycuda_driver.LogicError: cuMemAlloc failed: invalid argument
  </code></pre>
  <p>After further debugging it turns out <code>cuda.pagelocked_empty(size, dtype)</code> retuns [] at the output binding <em>separable_conv2d_29</em> with <em>size=0</em> and <em>dtype=numpy.float32</em>. With the running code, the size is &gt;0 for both input and output bindings.</p>