Fix crash in _CMapLookupCallback

core/src/fpdfapi/fpdf_parser/fpdf_parser_objects.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 "../../../include/fpdfapi/fpdf_parser.h"
 void CPDF_Object::Release()
 {
     if (m_ObjNum) {
@@ skipping 1253 matching lines @@
         return;
     }
     ((CPDF_Object*)value)->Destroy();
     m_IndirectObjs.RemoveKey((FX_LPVOID)(FX_UINTPTR)objnum);
 }
 void CPDF_IndirectObjects::InsertIndirectObject(FX_DWORD objnum, CPDF_Object* pObj)
 {
     if (objnum == 0 || pObj == NULL) {
         return;
     }
-    FX_LPVOID value;
+    FX_LPVOID value = NULL;
     if (m_IndirectObjs.Lookup((FX_LPVOID)(FX_UINTPTR)objnum, value)) {
-        ((CPDF_Object*)value)->Destroy();
+        if (value)
+        {
+            if (pObj->GetGenNum() <= ((CPDF_Object*)value)->GetGenNum())
+                return;
+            else 
+                ((CPDF_Object*)value)->Destroy();
+         }         
     }
     pObj->m_ObjNum = objnum;
     m_IndirectObjs.SetAt((FX_LPVOID)(FX_UINTPTR)objnum, pObj);
     if (m_LastObjNum < objnum) {
         m_LastObjNum = objnum;
     }
 }
 FX_DWORD CPDF_IndirectObjects::GetLastObjNum() const
 {
     return m_LastObjNum;
 }