Clean compiling warnings on Linux

xfa/src/fxbarcode/oned/BC_OnedUPCAWriter.h

 // 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
 
 #ifndef _BC_ONEDUPCAWRITER_H_
 #define _BC_ONEDUPCAWRITER_H_
 class CBC_Writer;
 class CBC_OnedEAN13Writer;
@@ skipping 10 matching lines @@
                   BCFORMAT format,
                   int32_t& outWidth,
                   int32_t& outHeight,
                   int32_t& e);
   uint8_t* Encode(const CFX_ByteString& contents,
                   BCFORMAT format,
                   int32_t& outWidth,
                   int32_t& outHeight,
                   int32_t hints,
                   int32_t& e);
+  uint8_t* Encode(const CFX_ByteString& contents,
+                  int32_t& outLength,
+                  int32_t& e) {
+    return nullptr;
+  }
   void RenderResult(const CFX_WideStringC& contents,
                     uint8_t* code,
                     int32_t codeLength,
                     FX_BOOL isDevice,
                     int32_t& e);
   FX_BOOL CheckContentValidity(const CFX_WideStringC& contents);
   CFX_WideString FilterContents(const CFX_WideStringC& contents);
   int32_t CalcChecksum(const CFX_ByteString& contents);
 
  protected:
   void ShowChars(const CFX_WideStringC& contents,
                  CFX_DIBitmap* pOutBitmap,
                  CFX_RenderDevice* device,
                  const CFX_Matrix* matrix,
                  int32_t barWidth,
                  int32_t multiple,
                  int32_t& e);
 };
 #endif