Vfx/fix/sgoperator create context drag (#28)

* Prevent from creating a context in VisualEffectSugraphOperator by draggingfrom an output slot.

* changelog

Author: iTris666

com.unity.visualeffectgraph/CHANGELOG.md

@@ -109,6 +109,7 @@ The version number for this package has increased due to a version update of a r
 - Prevent capacity from being 0 [Case 1233044](https://issuetracker.unity3d.com/product/unity/issues/guid/1233044/)
 - Fix for dragged parameters order when there are categories
 - Avoid NullReferenceException in Previous Position Binder" component. [Case 1242351](https://issuetracker.unity3d.com/product/unity/issues/guid/1242351/)
+- Prevent from creating a context in VisualEffectSugraphOperator by draggingfrom an output slot.
 
 ## [7.1.1] - 2019-09-05
 ### Added

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

@@ -297,7 +297,7 @@ void IEdgeConnectorListener.OnDropOutsidePort(Edge edge, Vector2 position)
             }
             else if (!exists)
             {
-                if (direction == Direction.Input)
+                if (direction == Direction.Input || viewController.model.visualEffectObject is VisualEffectSubgraphOperator) // no context for subgraph operators.
                     VFXFilterWindow.Show(VFXViewWindow.currentWindow, Event.current.mousePosition, view.ViewToScreenPosition(Event.current.mousePosition), new VFXNodeProvider(viewController, AddLinkedNode, ProviderFilter, new Type[] { typeof(VFXOperator), typeof(VFXParameter)}));
                 else
                     VFXFilterWindow.Show(VFXViewWindow.currentWindow, Event.current.mousePosition, view.ViewToScreenPosition(Event.current.mousePosition), new VFXNodeProvider(viewController, AddLinkedNode, ProviderFilter, new Type[] { typeof(VFXOperator), typeof(VFXParameter), typeof(VFXContext) }));