Add missing STDCALL for FPDFDoc_GetPageMode().

fpdfsdk/fpdf_ext.cpp

Index: fpdfsdk/fpdf_ext.cpp
diff --git a/fpdfsdk/fpdf_ext.cpp b/fpdfsdk/fpdf_ext.cpp
index 8a45a13e12046bb03897c732dc35d128c1b49a05..9bb54da59408030377e468bed078bf6c0ea5290f 100644
--- a/fpdfsdk/fpdf_ext.cpp
+++ b/fpdfsdk/fpdf_ext.cpp
@@ -191,7 +191,7 @@ void CheckUnSupportError(CPDF_Document* pDoc, uint32_t err_code) {
 #endif  // PDF_ENABLE_XFA
 }
 
-DLLEXPORT int FPDFDoc_GetPageMode(FPDF_DOCUMENT document) {
+DLLEXPORT int STDCALL FPDFDoc_GetPageMode(FPDF_DOCUMENT document) {
   CPDF_Document* pDoc = CPDFDocumentFromFPDFDocument(document);
   if (!pDoc)
     return PAGEMODE_UNKNOWN;