Added fix for rename bug with v2 AssetDatabase (#239)

* Added fix for NodeGraph rename bug with v2 AssetDatabase where renaming a graph asset can sometimes result in it being swapped as the main asset with one of the node sub assets.

Scripts/Editor/GraphRenameFixAssetProcessor.cs

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+using UnityEditor;
+using XNode;
+
+namespace XNodeEditor {
+    /// <summary>
+    /// This asset processor resolves an issue with the new v2 AssetDatabase system present on 2019.3 and later. When
+    /// renaming a <see cref="XNode.NodeGraph"/> asset, it appears that sometimes the v2 AssetDatabase will swap which asset
+    /// is the main asset (present at top level) between the <see cref="XNode.NodeGraph"/> and one of its <see cref="XNode.Node"/>
+    /// sub-assets. As a workaround until Unity fixes this, this asset processor checks all renamed assets and if it
+    /// finds a case where a <see cref="XNode.Node"/> has been made the main asset it will swap it back to being a sub-asset
+    /// and rename the node to the default name for that node type.
+    /// </summary>
+    internal sealed class GraphRenameFixAssetProcessor : AssetPostprocessor {
+        private static void OnPostprocessAllAssets(
+            string[] importedAssets,
+            string[] deletedAssets,
+            string[] movedAssets,
+            string[] movedFromAssetPaths) {
+            for (int i = 0; i < movedAssets.Length; i++) {
+                Node nodeAsset = AssetDatabase.LoadMainAssetAtPath(movedAssets[i]) as Node;
+
+                // If the renamed asset is a node graph, but the v2 AssetDatabase has swapped a sub-asset node to be its
+                // main asset, reset the node graph to be the main asset and rename the node asset back to its default
+                // name.
+                if (nodeAsset != null && AssetDatabase.IsMainAsset(nodeAsset)) {
+                    AssetDatabase.SetMainObject(nodeAsset.graph, movedAssets[i]);
+                    AssetDatabase.ImportAsset(movedAssets[i]);
+
+                    nodeAsset.name = NodeEditorUtilities.NodeDefaultName(nodeAsset.GetType());
+                    EditorUtility.SetDirty(nodeAsset);
+                }
+            }
+        }
+    }
+}

Scripts/Editor/GraphRenameFixAssetProcessor.cs.meta

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