Clean up XFA code which causes warnings

xfa/fxfa/parser/xfa_object_imp.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/parser/xfa_object.h"
 
 #include <memory>
 
@@ skipping 4486 matching lines @@
     for (; pNode; pNode = pNode->GetNodeItem(XFA_NODEITEM_NextSibling)) {
       const XFA_PROPERTY* pExistProperty =
           XFA_GetPropertyOfElement(eElement, pNode->GetClassID(), dwPacket);
       if (pExistProperty && (pExistProperty->uFlags & XFA_PROPERTYFLAG_OneOf)) {
         return NULL;
       }
     }
   }
   CXFA_Document* pFactory = m_pDocument->GetParser()->GetFactory();
   const XFA_PACKETINFO* pPacket = XFA_GetPacketByID(dwPacket);
-  CXFA_Node* pNewNode;
+  CXFA_Node* pNewNode = nullptr;
   for (; iCount <= index; iCount++) {
     pNewNode = pFactory->CreateNode(pPacket, eProperty);
     if (!pNewNode) {
       return NULL;
     }
     InsertChild(pNewNode, nullptr);
     pNewNode->SetFlag(XFA_NODEFLAG_Initialized, true);
   }
   return pNewNode;
 }
@@ skipping 847 matching lines @@
   return m_pAttachNode->InsertChild(pNewNode, pBeforeNode);
 }
 FX_BOOL CXFA_AttachNodeList::Remove(CXFA_Node* pNode) {
   return m_pAttachNode->RemoveChild(pNode);
 }
 CXFA_Node* CXFA_AttachNodeList::Item(int32_t iIndex) {
   return m_pAttachNode->GetChild(
       iIndex, XFA_ELEMENT_UNKNOWN,
       m_pAttachNode->GetClassID() == XFA_ELEMENT_Subform);
 }