Merge pull request #202 from Unity-Technologies/peter-fixes

Various fixes

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

     [Serializable]
     public class UVMaterialSlot : Vector2MaterialSlot, IMayRequireMeshUV
     {
-        private UVChannel m_Channel = UVChannel.UV0;
+        [SerializeField]
+        UVChannel m_Channel = UVChannel.UV0;
 
         public UVChannel channel
         {

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/PreviewManager.cs

             PropagateNodeSet(m_DirtyPreviews);
 
             m_NodesWith3DPreview.Clear();
-            foreach (var index in m_DirtyPreviews)
+            foreach (var node in m_Graph.GetNodes<AbstractMaterialNode>())
-                var node = (AbstractMaterialNode)m_Graph.GetNodeFromTempId(m_Identifiers[index]);
                 if (node.previewMode == PreviewMode.Preview3D)
                     m_NodesWith3DPreview.Add(node.tempId.index);
             }
         void DestroyRenderData(PreviewRenderData renderData)
         {
             if (renderData.shaderData != null
-                && renderData.shaderData.shader != null 
+                && renderData.shaderData.shader != null
-            
+
             if (renderData.shaderData != null && renderData.shaderData.node != null)
                 renderData.shaderData.node.onModified -= OnNodeModified;
         }