Don't convert property nodes to inline nodes during undo/redo (fixes #125)

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Data/Graphs/AbstractMaterialGraph.cs

 
         public void RemoveShaderProperty(Guid guid)
         {
+            var propertyNodes = GetNodes<PropertyNode>().Where(x => x.propertyGuid == guid).ToList();
+            foreach (var propNode in propertyNodes)
+                ReplacePropertyNodeWithConcreteNode(propNode);
+
+
-            var propertyNodes = GetNodes<PropertyNode>().Where(x => x.propertyGuid == guid).ToList();
-
-            foreach (var propNode in propertyNodes)
-                ReplacePropertyNodeWithConcreteNode(propNode);
-
             if (m_Properties.RemoveAll(x => x.guid == guid) > 0)
                 m_RemovedProperties.Add(guid);
         }
             {
                 vertexInputs.AddShaderChunk("float4 color : COLOR;", false);
             }
-            
+
             foreach (var channel in graphRequiements.requiresMeshUVs.Distinct())
             {
                 vertexInputs.AddShaderChunk(string.Format("float4 texcoord{0} : TEXCOORD{1};", ((int)channel).ToString(), vertexInputIndex.ToString()), false);