fix gradient serialization

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Presenters/GradientNodePresenter.cs

     [Serializable]
     class GradientContolPresenter : GraphControlPresenter
     {
+        [SerializeField]
+
+        [SerializeField]
+
+        [SerializeField]
+
         private UnityEngine.MaterialGraph.GradientNode prevnode;
 
         private string prevWindow = "";
             {
                 prevnode = cNode;
                 gradientobj = new GradientObject();
+                if (cNode.gradient != null)
+                {
+                    gradientobj.gradient = cNode.gradient;
+                }
+                
                 hserializedObject = new SerializedObject(gradientobj);
                 hcolorGradient = hserializedObject.FindProperty("gradient");
             }
         }
     }
 
+    [Serializable]
     public class GradientObject : ScriptableObject
     {
         public Gradient gradient = new Gradient();

MaterialGraphProject/Assets/_MingWai/GradientNode.cs

         [SerializeField]
         private Gradient m_gradient;
 
-        
         public Gradient gradient
         {
             get { return m_gradient; }

MaterialGraphProject/Assets/TestAssets/BW_logo.png.meta

+fileFormatVersion: 2
+guid: 8080b3773b9568a46bcaaf9b18512990
+timeCreated: 1495742078
+licenseType: Pro
+TextureImporter:
+  fileIDToRecycleName: {}
+  serializedVersion: 4
+  mipmaps:
+    mipMapMode: 0
+    enableMipMap: 0
+    sRGBTexture: 1
+    linearTexture: 0
+    fadeOut: 0
+    borderMipMap: 0
+    mipMapsPreserveCoverage: 0
+    alphaTestReferenceValue: 0.5
+    mipMapFadeDistanceStart: 1
+    mipMapFadeDistanceEnd: 3
+  bumpmap:
+    convertToNormalMap: 0
+    externalNormalMap: 0
+    heightScale: 0.25
+    normalMapFilter: 0
+  isReadable: 0
+  grayScaleToAlpha: 0
+  generateCubemap: 6
+  cubemapConvolution: 0
+  seamlessCubemap: 0
+  textureFormat: 1
+  maxTextureSize: 2048
+  textureSettings:
+    serializedVersion: 2
+    filterMode: -1
+    aniso: -1
+    mipBias: -1
+    wrapU: 1
+    wrapV: 1
+    wrapW: 1
+  nPOTScale: 1
+  lightmap: 0
+  compressionQuality: 50
+  spriteMode: 0
+  spriteExtrude: 1
+  spriteMeshType: 1
+  alignment: 0
+  spritePivot: {x: 0.5, y: 0.5}
+  spriteBorder: {x: 0, y: 0, z: 0, w: 0}
+  spritePixelsToUnits: 100
+  alphaUsage: 1
+  alphaIsTransparency: 1
+  spriteTessellationDetail: -1
+  textureType: 0
+  textureShape: 1
+  maxTextureSizeSet: 0
+  compressionQualitySet: 0
+  textureFormatSet: 0
+  platformSettings:
+  - buildTarget: DefaultTexturePlatform
+    maxTextureSize: 2048
+    resizeAlgorithm: 1
+    textureFormat: -1
+    textureCompression: 2
+    compressionQuality: 50
+    crunchedCompression: 0
+    allowsAlphaSplitting: 0
+    overridden: 0
+  - buildTarget: Standalone
+    maxTextureSize: 2048
+    resizeAlgorithm: 1
+    textureFormat: -1
+    textureCompression: 2
+    compressionQuality: 50
+    crunchedCompression: 0
+    allowsAlphaSplitting: 0
+    overridden: 0
+  spriteSheet:
+    serializedVersion: 2
+    sprites: []
+    outline: []
+    physicsShape: []
+  spritePackingTag: 
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

MaterialGraphProject/Assets/_MingWai/Gradient.ShaderGraph.meta

+fileFormatVersion: 2
+guid: 12adeac2a3368e94f9889377e4d426c2
+timeCreated: 1495742113
+licenseType: Pro
+ScriptedImporter:
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 
+  script: {fileID: 11500000, guid: 625f186215c104763be7675aa2d941aa, type: 3}

MaterialGraphProject/Assets/_MingWai/Gradient_Texture.ShaderGraph.meta

+fileFormatVersion: 2
+guid: ff2b03d7feb67a145835ad8adae9e0ad
+timeCreated: 1495742113
+licenseType: Pro
+ScriptedImporter:
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 
+  script: {fileID: 11500000, guid: 625f186215c104763be7675aa2d941aa, type: 3}