Fix segv above CPDFSDK_Document::GetPageView()

fpdfsdk/src/fpdfformfill.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 "../../public/fpdf_formfill.h"
 #include "../../public/fpdfview.h"
 #include "../../third_party/base/nonstd_unique_ptr.h"
 #include "../include/fsdk_define.h"
 #include "../include/fsdk_mgr.h"
 #include "../include/javascript/IJavaScript.h"
 
 namespace {
 
 CPDFSDK_Document* FormHandleToSDKDoc(FPDF_FORMHANDLE hHandle)
 {
     CPDFDoc_Environment* pEnv = (CPDFDoc_Environment*)hHandle;
     return pEnv ? pEnv->GetSDKDocument() : nullptr;
 }
 
 CPDFSDK_InterForm* FormHandleToInterForm(FPDF_FORMHANDLE hHandle)
 {
     CPDFSDK_Document* pSDKDoc = FormHandleToSDKDoc(hHandle);
     return pSDKDoc ? pSDKDoc->GetInterForm() : nullptr;
 }
 
 CPDFSDK_PageView* FormHandleToPageView(FPDF_FORMHANDLE hHandle, FPDF_PAGE page)
 {
+    if (!page)
+        return nullptr;
+
     CPDFSDK_Document* pSDKDoc = FormHandleToSDKDoc(hHandle);
     return pSDKDoc ? pSDKDoc->GetPageView((CPDF_Page*)page, TRUE) : nullptr;
 }
 
 }  // namespace
 
 DLLEXPORT int STDCALL FPDPage_HasFormFieldAtPoint(
     FPDF_FORMHANDLE hHandle, FPDF_PAGE page, double page_x, double page_y)
 {
     if (!page || !hHandle)
@@ skipping 268 matching lines @@
         {
             bExistCAAction = aa.ActionExist(CPDF_AAction::ClosePage);
             if (bExistCAAction)
             {
                 CPDF_Action action = aa.GetAction(CPDF_AAction::ClosePage);
                 pActionHandler->DoAction_Page(action, CPDF_AAction::ClosePage, pSDKDoc);
             }
         }
     }
 }