try fix crash when exiting editor with uiwidgets-based editor window openned

com.unity.uiwidgets/Runtime/rendering/binding.cs

             }, this.inEditorWindow);
         }
 
-        protected virtual void drawFrame() {
+        protected virtual void drawFrame(bool layoutOnly = false) {
+            if (layoutOnly) return;
+            
             this.pipelineOwner.flushCompositingBits();
             this.pipelineOwner.flushPaint();
             this.renderView.compositeFrame();

com.unity.uiwidgets/Runtime/widgets/binding.cs

 
         protected bool debugBuildingDirtyElements = false;
 
-        protected override void drawFrame() {
+        protected override void drawFrame(bool layoutOnly = false) {
             D.assert(!this.debugBuildingDirtyElements);
             D.assert(() => {
                 this.debugBuildingDirtyElements = true;
             }
             
             //The former widget tree must be layout first before its destruction
-            this.drawFrame();
+            this.drawFrame(true);
             this.attachRootWidget(null);
             this.buildOwner.buildScope(this._renderViewElement);
             this.buildOwner.finalizeTree();