Fix a security issue in FPDF_GetMetaText

fpdfsdk/src/fpdfdoc.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 "../include/fsdk_define.h"
 #include "../include/fpdfdoc.h"
 
 static int this_module = 0;
@@ skipping 231 matching lines @@
         CPDF_Document* pDoc = (CPDF_Document*)doc;
         // Get info dictionary
         CPDF_Dictionary* pInfo = pDoc->GetInfo();
         if (pInfo == NULL) return 0;
 
         CFX_WideString text = pInfo->GetUnicodeText(tag);
 
         // Use UTF-16LE encoding
         CFX_ByteString bstr = text.UTF16LE_Encode();
         unsigned long len = bstr.GetLength();
-        if (buffer != NULL || buflen >= len+2) {
+        if (buffer != NULL && buflen >= len+2) {
                 FXSYS_memcpy(buffer, (FX_LPCSTR)bstr, len);
                 // use double zero as trailer
                 ((FX_BYTE*)buffer)[len] = ((FX_BYTE*)buffer)[len+1] = 0;
         }
         return len+2;
 }