Fix crash in _CMapLookupCallback

core/src/fpdfapi/fpdf_parser/fpdf_parser_objects.cpp

Index: core/src/fpdfapi/fpdf_parser/fpdf_parser_objects.cpp
diff --git a/core/src/fpdfapi/fpdf_parser/fpdf_parser_objects.cpp b/core/src/fpdfapi/fpdf_parser/fpdf_parser_objects.cpp
index 6c93bcb39fd45f3401931b738274eb24fdda9abe..e945ab52a0010b5c1cc7c911b3a6596cec05a6ab 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_objects.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_objects.cpp
@@ -1271,9 +1271,15 @@ void CPDF_IndirectObjects::InsertIndirectObject(FX_DWORD objnum, CPDF_Object* pO
     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);