-Added const to a reference, should fix #2613

tools/editor/plugins/shader_graph_editor_plugin.cpp

@@ -1246,7 +1246,7 @@ void ShaderGraphView::_duplicate_nodes_request()
 
 }
 
-void ShaderGraphView::_duplicate_nodes(Array &p_nodes)
+void ShaderGraphView::_duplicate_nodes(const Array &p_nodes)
 {
 	List<int> n = List<int>();
 	for (int i=0; i<p_nodes.size();i++)

tools/editor/plugins/shader_graph_editor_plugin.h

@@ -149,7 +149,7 @@ class ShaderGraphView : public Node {
 	void _end_node_move();
 	void _move_node(int p_id,const Vector2& p_to);
 	void _duplicate_nodes_request();
-	void _duplicate_nodes(Array &p_nodes);
+    void _duplicate_nodes(const Array &p_nodes);
 	void _delete_nodes_request();