Fix a potential nullptr deref in CFX_MapPtrToPtr.

core/fxcrt/fx_basic_maps.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 "core/fxcrt/include/fx_basic.h"
 #include "core/fxcrt/plex.h"
 
 CFX_MapPtrToPtr::CFX_MapPtrToPtr(int nBlockSize)
-    : m_pHashTable(NULL),
+    : m_pHashTable(nullptr),
       m_nHashTableSize(17),
       m_nCount(0),
-      m_pFreeList(NULL),
-      m_pBlocks(NULL),
+      m_pFreeList(nullptr),
+      m_pBlocks(nullptr),
       m_nBlockSize(nBlockSize) {
   ASSERT(m_nBlockSize > 0);
 }
+
 void CFX_MapPtrToPtr::RemoveAll() {
   FX_Free(m_pHashTable);
-  m_pHashTable = NULL;
+  m_pHashTable = nullptr;
   m_nCount = 0;
-  m_pFreeList = NULL;
-  m_pBlocks->FreeDataChain();
-  m_pBlocks = NULL;
+  m_pFreeList = nullptr;
+  if (m_pBlocks) {
+    m_pBlocks->FreeDataChain();
+    m_pBlocks = nullptr;
+  }
 }
+
 CFX_MapPtrToPtr::~CFX_MapPtrToPtr() {
   RemoveAll();
   ASSERT(m_nCount == 0);
 }
 uint32_t CFX_MapPtrToPtr::HashKey(void* key) const {
   return ((uint32_t)(uintptr_t)key) >> 4;
 }
 void CFX_MapPtrToPtr::GetNextAssoc(FX_POSITION& rNextPosition,
                                    void*& rKey,
                                    void*& rValue) const {
@@ skipping 19 matching lines @@
 }
 FX_BOOL CFX_MapPtrToPtr::Lookup(void* key, void*& rValue) const {
   uint32_t nHash;
   CAssoc* pAssoc = GetAssocAt(key, nHash);
   if (!pAssoc) {
     return FALSE;
   }
   rValue = pAssoc->value;
   return TRUE;
 }
+
 void* CFX_MapPtrToPtr::GetValueAt(void* key) const {
   uint32_t nHash;
   CAssoc* pAssoc = GetAssocAt(key, nHash);
-  if (!pAssoc) {
-    return NULL;
-  }
-  return pAssoc->value;
+  return pAssoc ? pAssoc->value : nullptr;
 }
+
 void*& CFX_MapPtrToPtr::operator[](void* key) {
   uint32_t nHash;
   CAssoc* pAssoc;
   if ((pAssoc = GetAssocAt(key, nHash)) == NULL) {
     if (!m_pHashTable) {
       InitHashTable(m_nHashTableSize);
     }
     pAssoc = NewAssoc();
     pAssoc->key = key;
     pAssoc->pNext = m_pHashTable[nHash];
@@ skipping 63 matching lines @@
 }
 void CFX_MapPtrToPtr::FreeAssoc(CFX_MapPtrToPtr::CAssoc* pAssoc) {
   pAssoc->pNext = m_pFreeList;
   m_pFreeList = pAssoc;
   m_nCount--;
   ASSERT(m_nCount >= 0);
   if (m_nCount == 0) {
     RemoveAll();
   }
 }