message: fix concat issue related to negative input concat_dim
diff: @@ -598,7 +598,6 @@ class MklConcatOp : public OpKernel {
  concat_dim_tensor.shape().DebugString()));
  int32 concat_dim = internal::SubtleMustCopy(
  concat_dim_tensor.scalar<int32>()());
  - if (concat_dim < 0) concat_dim = N + concat_dim;
  // check that ranks of all tensors match
  // and that their shapes match except for concat_dim.
  @@ -609,6 +608,9 @@ class MklConcatOp : public OpKernel {
  input_shapes[0].GetTfShape() :
  input_tensors[0].shape();
  size_t expected_dims = expected_shape.dims();
  +
  + if (concat_dim < 0) concat_dim = expected_dims + concat_dim;
  +
  for (auto& s : input_shapes) {
  if (s == expected_shape) {++i; continue;}
  