Remove ownership of CPDFSDK_Document from CPDFXFA_Document

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 240 matching lines @@
   if (hWidget->CanCut())
     menuFlag |= FXFA_MENU_CUT;
   if (hWidget->CanSelectAll())
     menuFlag |= FXFA_MENU_SELECTALL;
 
   return pEnv->PopupMenu(pPage, hWidget, menuFlag, ptPopup);
 }
 
 void CPDFXFA_DocEnvironment::PageViewEvent(CXFA_FFPageView* pPageView,
                                            uint32_t dwFlags) {
-  CPDFSDK_Environment* pEnv = m_pDocument->GetSDKDoc()->GetEnv();
+  CPDFSDK_Document* pSDKDoc = m_pDocument->GetSDKDoc();
+  if (!pSDKDoc)
+    return;
+
+  CPDFSDK_Environment* pEnv = pSDKDoc->GetEnv();
   if (!pEnv)
     return;
 
   if (m_pDocument->GetLoadStatus() == FXFA_LOADSTATUS_LOADING ||
       m_pDocument->GetLoadStatus() == FXFA_LOADSTATUS_CLOSING ||
       XFA_PAGEVIEWEVENT_StopLayout != dwFlags)
     return;
 
   int nNewCount = m_pDocument->GetPageCount();
   if (nNewCount == m_pDocument->GetOriginalPageCount())
@@ skipping 739 matching lines @@
   if (!m_pJSContext) {
     m_pDocument->GetSDKDoc()->GetEnv()->GetJSRuntime()->SetReaderDocument(
         m_pDocument->GetSDKDoc());
     m_pJSContext =
         m_pDocument->GetSDKDoc()->GetEnv()->GetJSRuntime()->NewContext();
   }
 
   return m_pDocument->GetSDKDoc()->GetEnv()->GetJSRuntime()->GetValueByName(
       szPropName, pValue);
 }