Fix edge case with editor pasting (#2145)

This changelist fixes the edge case of pasting with an empty copy buffer in the Graph Editor.

Previously, this action would have an unintended effect on node positions, and it now has no impact on the graph.

source/MaterialXGraphEditor/Graph.cpp

@@ -4045,8 +4045,8 @@ void Graph::drawGraph(ImVec2 mousePos)
                     for (std::map<UiNodePtr, UiNodePtr>::iterator iter = _copiedNodes.begin(); iter != _copiedNodes.end(); iter++)
                     {
                         copyUiNode(iter->first);
+                        _addNewNode = true;
                     }
-                    _addNewNode = true;
                 }
                 else
                 {