Fix some iterator invalidation issues while traversing CPDF_Dictionary.

fpdfsdk/src/fpdfppo.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 "public/fpdf_ppo.h"
 
 #include <memory>
 
@@ skipping 195 matching lines @@
     case PDFOBJ_REFERENCE: {
       CPDF_Reference* pReference = pObj->AsReference();
       FX_DWORD newobjnum = GetNewObjId(pDoc, pObjNumberMap, pReference);
       if (newobjnum == 0)
         return FALSE;
       pReference->SetRef(pDoc, newobjnum);
       break;
     }
     case PDFOBJ_DICTIONARY: {
       CPDF_Dictionary* pDict = pObj->AsDictionary();
-      for (const auto& it : *pDict) {
-        const CFX_ByteString& key = it.first;
-        CPDF_Object* pNextObj = it.second;
+      auto it = pDict->begin();
+      while (it != pDict->end()) {
+        const CFX_ByteString& key = it->first;
+        CPDF_Object* pNextObj = it->second;
+        ++it;
         if (!FXSYS_strcmp(key, "Parent") || !FXSYS_strcmp(key, "Prev") ||
             !FXSYS_strcmp(key, "First")) {
           continue;
         }
         if (pNextObj) {
           if (!UpdateReference(pNextObj, pDoc, pObjNumberMap))
             pDict->RemoveAt(key);
         } else {
           return FALSE;
         }
@@ skipping 167 matching lines @@
   if (!pSrcDict)
     return FALSE;
 
   CPDF_Dictionary* pDstDict = pDstDoc->GetRoot();
   if (!pDstDict)
     return FALSE;
 
   pDstDict->SetAt("ViewerPreferences", pSrcDict->Clone(TRUE));
   return TRUE;
 }