Fix open prefab showing nothing problem.

Author: Yuncong Zhang

Runtime/editor/editor_window.cs

@@ -166,8 +166,6 @@ protected virtual TimeSpan getTime() {
 
         void updatePhysicalSize() {
             var size = this.queryWindowSize();
-            this._lastWindowWidth = size.x;
-            this._lastWindowHeight = size.y;
             this._physicalSize = new Size(
                 this._lastWindowWidth * this._devicePixelRatio,
                 this._lastWindowHeight * this._devicePixelRatio);