Revert "Remove FX_Alloc() null checks now that it can't return NULL."

core/src/fxcrt/fx_basic_wstring.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 <stddef.h>  // For offsetof().
 
 #include "../../include/fxcrt/fx_basic.h"
 #include "../../../third_party/base/numerics/safe_math.h"
@@ skipping 16 matching lines @@
     // Now round to an 8-byte boundary. We'd expect that this is the minimum
     // granularity of any of the underlying allocators, so there may be cases
     // where we can save a re-alloc when adding a few characters to a string
     // by using this otherwise wasted space.
     iSize += 7;
     int totalSize = iSize.ValueOrDie() & ~7;
     int usableLen = (totalSize - overhead) / sizeof(FX_WCHAR);
     FXSYS_assert(usableLen >= nLen);
 
     void* pData = FX_Alloc(FX_BYTE, iSize.ValueOrDie());
+    if (!pData) {
+        return NULL;
+    }
     return new (pData) StringData(nLen, usableLen);
 }
 CFX_WideString::~CFX_WideString()
 {
     if (m_pData) {
         m_pData->Release();
     }
 }
 CFX_WideString::CFX_WideString(const CFX_WideString& stringSrc)
 {
@@ skipping 1030 matching lines @@
             return (CFX_CharMap*)&g_DefaultJISMapper;
         case 936:
             return (CFX_CharMap*)&g_DefaultGBKMapper;
         case 949:
             return (CFX_CharMap*)&g_DefaultUHCMapper;
         case 950:
             return (CFX_CharMap*)&g_DefaultBig5Mapper;
     }
     return NULL;
 }