Make reset reference menu appear only when reference name is overridden

com.unity.shadergraph/Editor/Data/Graphs/AbstractMaterialGraph.cs

             return displayName;
         }
 
-        public string SanitizePropertyReferenceName(string referenceName)
+        public string SanitizePropertyReferenceName(string referenceName, Guid guid = default(Guid))
+
+            if (string.IsNullOrEmpty(referenceName))
+                return null;
+
+            if (!referenceName.StartsWith("_"))
+                referenceName = "_" + referenceName;
+
-            // Similat to teh property names, duplicate names are handled by appending `_n`
+            // Similar to the property names, duplicate names are handled by appending `_n`
             // to the end of the referene name.
             if (m_Properties.Any(p => p.referenceName == referenceName && p.guid != guid))
             {