fix crash when editor closes

Author: zhuxingwei

Runtime/editor/editor_window.cs

@@ -15,10 +15,33 @@ namespace Unity.UIWidgets.editor {
 #if UNITY_EDITOR
     public abstract class UIWidgetsEditorWindow : EditorWindow, WindowHost {
         WindowAdapter _windowAdapter;
-
+        
+        static readonly List<UIWidgetsEditorWindow> _activeEditorWindows = new List<UIWidgetsEditorWindow>();
+
+        [InitializeOnLoadMethod]
+        static void _OnBaseEditorWindowLoaded()
+        {
+            EditorApplication.quitting += () =>
+            {
+                foreach (var editorWindow in _activeEditorWindows) {
+                    editorWindow.OnDisable();
+                }
+                
+                _activeEditorWindows.Clear();
+            };
+        }
+        
         public UIWidgetsEditorWindow() {
             this.wantsMouseMove = true;
             this.wantsMouseEnterLeaveWindow = true;
+            
+            _activeEditorWindows.Add(this);
+        }
+        
+        void OnDestroy() {
+            if (_activeEditorWindows.Contains(this)) {
+                _activeEditorWindows.Remove(this);
+            }
         }
 
         protected virtual void OnEnable() {