message: Enable the n=1 special case in the DeserializeSparse op.
  The optimized case was previously dead because of two off-by-one errors (mea culpa).
diff: @@ -340,7 +340,7 @@ class DeserializeSparseOp : public OpKernel {
  "but has a zero dimension ",
  serialized_sparse.shape().DebugString()));
  - if (num_sparse_tensors == 0 && serialized_sparse.shape().dims() == 1) {
  + if (num_sparse_tensors == 1 && serialized_sparse.shape().dims() == 0) {
  // Special case with a single sparse tensor. We can avoid data
  // motion in the Concat and Reshape.
  const auto& serialized_sparse_t = serialized_sparse.vec<T>();
  