Fix op constant_pad_nd (#708)

Summary:
Pull Request resolved: #708

Fix for zero rank tensor
ghstack-source-id: 203341585
exported-using-ghexport

Reviewed By: SS-JIA

Differential Revision: D49849625

fbshipit-source-id: 4b01ed70f03a1552047e11849482aa035bde80d5

Author: manuelcandales

kernels/portable/cpu/op_constant_pad_nd.cpp

@@ -145,6 +145,11 @@ void constant_pad_nd_out_impl(
 
   size_t ndim = self.dim();
 
+  if (ndim == 0) {
+    out_data[0] = self_data[0];
+    return;
+  }
+
   int64_t self_sizes[kTensorDimensionLimit];
   int64_t self_strides[kTensorDimensionLimit];
   int64_t out_sizes[kTensorDimensionLimit];