Fix for displaying error from the creation of a node.

Author: iTris666

com.unity.visualeffectgraph/Editor/GraphView/Elements/VFXContextUI.cs

@@ -602,6 +602,8 @@ public void RefreshContext()
                             blockUI = InstantiateBlock(blockController);
                             m_BlockContainer.Add(blockUI);
                             m_BlockContainer.Insert(prevBlock == null ? 0 : m_BlockContainer.IndexOf(prevBlock) + 1, blockUI);
+                            //Refresh error can only be called after the block has been instanciated
+                            blockController.model.RefreshErrors(controller.viewController.graph);
                         }
                         prevBlock = blockUI;
                     }

com.unity.visualeffectgraph/Editor/GraphView/Elements/VFXNodeUI.cs

@@ -36,7 +36,6 @@ public VFXNodeController controller
                 OnNewController();
                 if (m_Controller != null)
                 {
-                    controller.model.RefreshErrors(controller.viewController.graph);
                     m_Controller.RegisterHandler(this);
                 }
             }

com.unity.visualeffectgraph/Editor/GraphView/Views/VFXView.cs

@@ -600,6 +600,8 @@ private void RegisterError(VFXModel model, VFXErrorOrigin errorOrigin,string err
                 if (nodeController == null)
                     return;
                 target = GetNodeByController(nodeController);
+                if (target == null)
+                    return;
                 targetParent = target.parent;
                 target = (target as VFXNodeUI).titleContainer;
                 alignement = SpriteAlignment.LeftCenter;
@@ -1079,6 +1081,7 @@ void SyncNodes()
                         needOneListenToGeometry = false;
                         newElement.RegisterCallback<GeometryChangedEvent>(OnOneNodeGeometryChanged);
                     }
+                    newElement.controller.model.RefreshErrors(controller.graph);
                 }
                 Profiler.EndSample();