Fix layering violation in CPDF_Document::FromFPDFDocument().

fpdfsdk/src/fpdf_dataavail.cpp

Index: fpdfsdk/src/fpdf_dataavail.cpp
diff --git a/fpdfsdk/src/fpdf_dataavail.cpp b/fpdfsdk/src/fpdf_dataavail.cpp
index 3944f67b03aa1ba54060576f398cc9cba9098710..b7b42ab32a6fcfe2bff7686e33e26bde0477db70 100644
--- a/fpdfsdk/src/fpdf_dataavail.cpp
+++ b/fpdfsdk/src/fpdf_dataavail.cpp
@@ -115,7 +115,7 @@ FPDFAvail_GetDocument(FPDF_AVAIL avail, FPDF_BYTESTRING password) {
 }
 
 DLLEXPORT int STDCALL FPDFAvail_GetFirstPageNum(FPDF_DOCUMENT doc) {
-  CPDF_Document* pDoc = CPDF_Document::FromFPDFDocument(doc);
+  CPDF_Document* pDoc = CPDFDocumentFromFPDFDocument(doc);
   if (!doc)
     return 0;
   return ((CPDF_Parser*)pDoc->GetParser())->GetFirstPageNo();