Fix some return FALSE in functions that return pointers

fpdfsdk/fpdfxfa/cpdfxfa_docenvironment.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 "fpdfsdk/fpdfxfa/cpdfxfa_docenvironment.h"
 
 #include "core/fpdfapi/parser/cpdf_array.h"
 #include "core/fpdfapi/parser/cpdf_stream_acc.h"
@@ skipping 691 matching lines @@
   FX_BOOL ret = SubmitDataInternal(hDoc, submit);
   NotifySubmit(FALSE);
   return ret;
 }
 
 IFX_SeekableReadStream* CPDFXFA_DocEnvironment::OpenLinkedFile(
     CXFA_FFDoc* hDoc,
     const CFX_WideString& wsLink) {
   CPDFSDK_FormFillEnvironment* pFormFillEnv = m_pDocument->GetFormFillEnv();
   if (!pFormFillEnv)
-    return FALSE;
+    return nullptr;
 
   CFX_ByteString bs = wsLink.UTF16LE_Encode();
   int len = bs.GetLength();
   FPDF_FILEHANDLER* pFileHandler =
       pFormFillEnv->OpenFile(0, (FPDF_WIDESTRING)bs.GetBuffer(len), "rb");
   bs.ReleaseBuffer(len);
-
   if (!pFileHandler)
     return nullptr;
+
   return new CFPDF_FileStream(pFileHandler);
 }
 
 FX_BOOL CPDFXFA_DocEnvironment::ExportSubmitFile(FPDF_FILEHANDLER* pFileHandler,
                                                  int fileType,
                                                  FPDF_DWORD encodeType,
                                                  FPDF_DWORD flag) {
   if (!m_pDocument->GetXFADocView())
     return FALSE;
 
@@ skipping 293 matching lines @@
       !m_pDocument->GetFormFillEnv()->GetJSRuntime()) {
     return FALSE;
   }
 
   CPDFSDK_FormFillEnvironment* pFormFillEnv = m_pDocument->GetFormFillEnv();
   if (!m_pJSContext)
     m_pJSContext = pFormFillEnv->GetJSRuntime()->NewContext();
 
   return pFormFillEnv->GetJSRuntime()->GetValueByName(szPropName, pValue);
 }