Fix input area rendering

packages/cells/src/inputarea.ts

@@ -116,9 +116,8 @@ class InputArea extends Widget {
     let layout = this.layout as PanelLayout;
     if (this._rendered) {
       this._rendered.parent = null;
-    } else {
-      this._editor.parent = null;
     }
+    this._editor.parent = null;
     this._rendered = widget;
     layout.addWidget(widget);
   }
@@ -130,8 +129,8 @@ class InputArea extends Widget {
     let layout = this.layout as PanelLayout;
     if (this._rendered) {
       this._rendered.parent = null;
-      layout.addWidget(this._editor);
     }
+    layout.addWidget(this._editor);
   }
 
   /**