Fix setup of input tensor in spatialtf_sampler

theano/gpuarray/c_code/spatialtf_sampler.c

@@ -94,8 +94,25 @@ spatialtf_sampler(PyGpuArrayObject * input,
         return -1;
     }
 
+    // In the input tensor, we must use its width and height, instead
+    // of the grid's width and height. The number of images and channels
+    // should be the same as the grid dimensions
+    const int input_num_images = (int) PyGpuArray_DIM( input, 0 );
+    const int input_height = (int) PyGpuArray_DIM( input, 1 );
+    const int input_width = (int) PyGpuArray_DIM( input, 2 );
+    const int input_num_channels = (int) PyGpuArray_DIM( input, 3 );
+
+    if ( input_num_images != num_images ||
+         input_num_channels != num_channels )
+    {
+        PyErr_Format( PyExc_RuntimeError,
+                      "Input should have %d images and %d channels, got %d images and %d channels.",
+                       num_images, num_channels, input_num_images, input_num_channels );
+        return -1;
+    }
+
     err = cudnnSetTensor4dDescriptor( spatialtf_ctx.xdesc, tf, dt, num_images,
-        num_channels, height, width );
+        num_channels, input_height, input_width );
 
     if ( err != CUDNN_STATUS_SUCCESS )
     {