Re-enable CHECK() than only 0-numbered objects are released

core/fpdfapi/parser/cpdf_object.cpp

 // Copyright 2016 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 "core/fpdfapi/parser/cpdf_object.h"
 
 #include <algorithm>
 
@@ skipping 20 matching lines @@
   return CloneObjectNonCyclic(true);
 }
 
 CPDF_Object* CPDF_Object::CloneNonCyclic(
     bool bDirect,
     std::set<const CPDF_Object*>* pVisited) const {
   return Clone();
 }
 
 void CPDF_Object::Release() {
-  if (m_ObjNum)
-    return;
-
+  CHECK(!m_ObjNum);
   delete this;
 }
 
 CFX_ByteString CPDF_Object::GetString() const {
   return CFX_ByteString();
 }
 
 CFX_WideString CPDF_Object::GetUnicodeText() const {
   return CFX_WideString();
 }
@@ skipping 102 matching lines @@
   return nullptr;
 }
 
 CPDF_String* CPDF_Object::AsString() {
   return nullptr;
 }
 
 const CPDF_String* CPDF_Object::AsString() const {
   return nullptr;
 }