Clean up XFA code which causes warnings

xfa/fxfa/parser/xfa_parser_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_parser_imp.h"
 
 #include <memory>
 
@@ skipping 344 matching lines @@
     case XFA_XDPPACKET_Xdc:
       return ParseAsXDPPacket_Xdc(pXMLDocumentNode, ePacketID);
     case XFA_XDPPACKET_LocaleSet:
     case XFA_XDPPACKET_ConnectionSet:
     case XFA_XDPPACKET_SourceSet:
       return ParseAsXDPPacket_LocaleConnectionSourceSet(pXMLDocumentNode,
                                                         ePacketID);
     default:
       return ParseAsXDPPacket_User(pXMLDocumentNode, ePacketID);
   }
-  return NULL;
 }
 CXFA_Node* CXFA_SimpleParser::ParseAsXDPPacket_XDP(
     CFDE_XMLNode* pXMLDocumentNode,
     XFA_XDPPACKET ePacketID) {
   if (!XFA_FDEExtension_MatchNodeName(
           pXMLDocumentNode, XFA_GetPacketByIndex(XFA_PACKET_XDP)->pName,
           XFA_GetPacketByIndex(XFA_PACKET_XDP)->pURI,
           XFA_GetPacketByIndex(XFA_PACKET_XDP)->eFlags)) {
     return nullptr;
   }
@@ skipping 1179 matching lines @@
     }
     if (pPause && iCount > 500 && pPause->NeedToPauseNow()) {
       break;
     }
   }
   return (m_syntaxParserResult == FDE_XmlSyntaxResult::Error ||
           m_NodeStack.GetSize() != 1)
              ? -1
              : m_pParser->GetStatus();
 }