Remove ownership of CPDFSDK_Document from CPDFXFA_Document

fpdfsdk/fpdfxfa/cpdfxfa_docenvironment.cpp

Index: fpdfsdk/fpdfxfa/cpdfxfa_docenvironment.cpp
diff --git a/fpdfsdk/fpdfxfa/cpdfxfa_docenvironment.cpp b/fpdfsdk/fpdfxfa/cpdfxfa_docenvironment.cpp
index 1b27e16551ad58cca44d16fa9466b7fbc2d17caf..fed54096246f4d2c1197f11e2e149ba564634624 100644
--- a/fpdfsdk/fpdfxfa/cpdfxfa_docenvironment.cpp
+++ b/fpdfsdk/fpdfxfa/cpdfxfa_docenvironment.cpp
@@ -258,7 +258,11 @@ FX_BOOL CPDFXFA_DocEnvironment::PopupMenu(CXFA_FFWidget* hWidget,
 
 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;