Update pyfunc.cc for the prefast warning. (#545)

* Update pyfunc.cc for the prefast warning.

* address a comment

pyop/pyfunc.cc

@@ -399,9 +399,9 @@ void PyCustomOpDef::AddOp(const PyCustomOpDef* cod) {
 
   // No need to protect against concurrent access, GIL is doing that.
   auto val = std::make_pair(op_domain, std::vector<PyCustomOpFactory>());
-  const auto [it_domain_op, success] = PyOp_container().insert(val);
+  auto [it_domain_op, success] = PyOp_container().insert(val);
   assert(success || !it_domain_op->second.empty());
-  it_domain_op->second.emplace_back(PyCustomOpFactory(cod, op_domain, op));
+  it_domain_op->second.emplace_back(cod, op_domain, op);
 }
 
 const PyCustomOpFactory* PyCustomOpDef_FetchPyCustomOps(size_t num) {