Clean up XFA code which causes warnings

xfa/fxfa/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 "xfa/fxfa/app/xfa_ffwidgetacc.h"
 
 #include <algorithm>
 #include <memory>
@@ skipping 695 matching lines @@
   CXFA_LayoutItem* pLayout = nullptr;
   if (pWidget) {
     pLayout = pWidget->GetNext();
   } else {
     pLayout = m_pDocView->GetXFALayout()->GetLayoutItem(m_pNode);
   }
   return static_cast<CXFA_FFWidget*>(pLayout);
 }
 void CXFA_WidgetAcc::UpdateUIDisplay(CXFA_FFWidget* pExcept) {
   CXFA_FFWidget* pWidget = NULL;
-  while ((pWidget = GetNextWidget(pWidget))) {
+  while ((pWidget = GetNextWidget(pWidget)) != nullptr) {
     if (pWidget == pExcept || !pWidget->IsLoaded() ||
         (GetUIType() != XFA_ELEMENT_CheckButton && pWidget->IsFocused())) {
       continue;
     }
     pWidget->UpdateFWLData();
     pWidget->AddInvalidateRect();
   }
 }
 
 void CXFA_WidgetAcc::CalcCaptionSize(CFX_SizeF& szCap) {
@@ skipping 964 matching lines @@
     if (pIDNode) {
       pEmbAcc = (CXFA_WidgetAcc*)pIDNode->GetWidgetData();
     }
     if (pEmbAcc) {
       pEmbAcc->GetValue(wsValue, XFA_VALUEPICTURE_Display);
       return TRUE;
     }
   }
   return FALSE;
 }