Change GetOutputElement to use delayed validation (#1964)

* Change GetOutputElement to use delayed validation

* Cleanup

src/ngraph/op/get_output_element.cpp

@@ -26,11 +26,15 @@ op::GetOutputElement::GetOutputElement(const shared_ptr<Node>& arg, size_t n)
     , m_n{n}
 {
     constructor_validate_and_infer_types();
-    NODE_VALIDATION_ASSERT(this, m_n < arg->get_output_size())
-        << "Output at index " << m_n << " requested, but argument has only "
-        << arg->get_output_size() << " outputs.";
+}
+
+void op::GetOutputElement::validate_and_infer_types()
+{
+    NODE_VALIDATION_ASSERT(this, m_n < get_input_size())
+        << "Output at index " << m_n << " requested, but node has only " << get_input_size()
+        << " inputs.";
 
-    set_output_type(0, arg->get_output_element_type(n), arg->get_output_partial_shape(n));
+    set_output_type(0, get_input_element_type(m_n), get_input_partial_shape(m_n));
 }
 
 shared_ptr<Node> op::GetOutputElement::copy_with_new_args(const NodeVector& new_args) const

src/ngraph/op/get_output_element.hpp

@@ -36,6 +36,7 @@ namespace ngraph
 
             virtual std::shared_ptr<Node>
                 copy_with_new_args(const NodeVector& new_args) const override;
+            void validate_and_infer_types() override;
 
             /// \return The index of the tuple element to get.
             size_t get_n() const { return m_n; }