[shader graph] Fix edge connection so that it removes input edges before connecting new input edges.

UnityProject/Assets/UnityShaderEditor/Editor/Source/BaseMaterialGraph.cs

 
         public override Edge Connect(Slot fromSlot, Slot toSlot)
         {
-            var edge = base.Connect(fromSlot, toSlot);
+            Slot outputSlot = null;
+            Slot inputSlot = null;
+
+            // output must connect to input
+            if (fromSlot.isOutputSlot)
+                outputSlot = fromSlot;
+            else if (fromSlot.isInputSlot)
+                inputSlot = fromSlot;
+
+            if (toSlot.isOutputSlot)
+                outputSlot = toSlot;
+            else if (toSlot.isInputSlot)
+                inputSlot = toSlot;
+
+            if (inputSlot == null || outputSlot == null)
+                return null;
+
+            // remove any inputs that exits before adding
+            foreach (var edge in inputSlot.edges.ToArray())
+            {
+                Debug.Log("Removing edge:" + edge);
+                // call base here as we DO NOT want to
+                // do expensive shader regeneration
+                base.RemoveEdge(edge);
+            }
+            
+            var newEdge = base.Connect(fromSlot, toSlot);
+            
+            Debug.Log("Connected edge: " + newEdge);
-                return edge;
+                return newEdge;
-            return edge;
+            return newEdge;
         }
 
         public override void AddNode(Node node)

UnityProject/Assets/UnityShaderEditor/Editor/Source/Drawing/MaterialGraphDataSource.cs

             }
 
             e.ParentCanvas().ReloadData();
+            e.ParentCanvas().Repaint();
-            Debug.Log("Connecting: " + a + " " + b);
-            //m_Elements.Add();
         }
     }
 }