Call CXFA_Object::ToNode() rather than C-style casting.

xfa/src/fxfa/src/app/xfa_ffwidgetacc.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include <algorithm>
 
 #include "xfa/src/foxitlib.h"
 #include "xfa/src/fxfa/src/common/xfa_common.h"
@@ skipping 1683 matching lines @@
     CXFA_Node* pWidgetNode = m_pWidgetAcc->GetNode();
     CXFA_Node* pParent = pWidgetNode->GetNodeItem(XFA_NODEITEM_Parent);
     CXFA_Document* pDocument = pWidgetNode->GetDocument();
     CXFA_Node* pIDNode = NULL;
     CXFA_WidgetAcc* pEmbAcc = NULL;
     if (pParent) {
       pIDNode = pDocument->GetNodeByID(pParent, wsAttr);
     }
     if (!pIDNode) {
       pIDNode = pDocument->GetNodeByID(
-          (CXFA_Node*)pDocument->GetXFAObject(XFA_HASHCODE_Form), wsAttr);
+          ToNode(pDocument->GetXFAObject(XFA_HASHCODE_Form)), wsAttr);
     }
     if (pIDNode) {
       pEmbAcc = (CXFA_WidgetAcc*)pIDNode->GetWidgetData();
     }
     if (pEmbAcc) {
       pEmbAcc->GetValue(wsValue, XFA_VALUEPICTURE_Display);
       return TRUE;
     }
   }
   return FALSE;
 }