Add a missing initialisation for CPDF_ContentMarkItem.

core/fpdfapi/fpdf_page/cpdf_contentmarkitem.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/fpdf_page/cpdf_contentmarkitem.h"
 
 #include "core/fpdfapi/fpdf_parser/include/cpdf_dictionary.h"
 
-CPDF_ContentMarkItem::CPDF_ContentMarkItem() {
-  m_ParamType = None;
-}
+CPDF_ContentMarkItem::CPDF_ContentMarkItem()
+    : m_ParamType(None), m_pParam(nullptr) {}
 
 CPDF_ContentMarkItem::CPDF_ContentMarkItem(const CPDF_ContentMarkItem& src) {
   m_MarkName = src.m_MarkName;
   m_ParamType = src.m_ParamType;
   if (m_ParamType == DirectDict) {
     m_pParam = ToDictionary(src.m_pParam->Clone());
   } else {
     m_pParam = src.m_pParam;
   }
 }
 
 CPDF_ContentMarkItem::~CPDF_ContentMarkItem() {
   if (m_ParamType == DirectDict && m_pParam)
     m_pParam->Release();
 }
 
 FX_BOOL CPDF_ContentMarkItem::HasMCID() const {
   if (m_pParam &&
       (m_ParamType == DirectDict || m_ParamType == PropertiesDict)) {
     return m_pParam->KeyExist("MCID");
   }
   return FALSE;
 }