Introduce CPDF_Document::FromFPDFDocument().

fpdfsdk/src/fpdfeditimg.cpp

Index: fpdfsdk/src/fpdfeditimg.cpp
diff --git a/fpdfsdk/src/fpdfeditimg.cpp b/fpdfsdk/src/fpdfeditimg.cpp
index bb710789ccdc5c1c8fa391def31581365f93ad77..ef0576b6027cbc657ff92b5c6acf6f77c46850ca 100644
--- a/fpdfsdk/src/fpdfeditimg.cpp
+++ b/fpdfsdk/src/fpdfeditimg.cpp
@@ -9,10 +9,11 @@
 
 DLLEXPORT FPDF_PAGEOBJECT STDCALL
 FPDFPageObj_NewImgeObj(FPDF_DOCUMENT document) {
-  if (!document)
-    return NULL;
+  CPDF_Document* pDoc = CPDF_Document::FromFPDFDocument(document);
+  if (!pDoc)
+    return nullptr;
   CPDF_ImageObject* pImageObj = new CPDF_ImageObject;
-  CPDF_Image* pImg = new CPDF_Image((CPDF_Document*)document);
+  CPDF_Image* pImg = new CPDF_Image(pDoc);
   pImageObj->m_pImage = pImg;
   return pImageObj;
 }