Remove dead code from CPDF_Metadata. Add missing nullptr check.

fpdfsdk/src/fpdf_ext.cpp

Index: fpdfsdk/src/fpdf_ext.cpp
diff --git a/fpdfsdk/src/fpdf_ext.cpp b/fpdfsdk/src/fpdf_ext.cpp
index e95a2f00947e8b8b7363e4759d8e9fddac90a0cc..2d84ff2a507231af0e0432d69333157dc57cd919 100644
--- a/fpdfsdk/src/fpdf_ext.cpp
+++ b/fpdfsdk/src/fpdf_ext.cpp
@@ -88,7 +88,7 @@ void CheckUnSupportAnnot(CPDF_Document* pDoc, CPDF_Annot* pPDFAnnot) {
   }
 }
 
-FX_BOOL CheckSharedForm(CXML_Element* pElement, CFX_ByteString cbName) {
+FX_BOOL CheckSharedForm(const CXML_Element* pElement, CFX_ByteString cbName) {
   int count = pElement->CountAttrs();
   int i = 0;
   for (i = 0; i < count; i++) {
@@ -169,9 +169,8 @@ void CheckUnSupportError(CPDF_Document* pDoc, FX_DWORD err_code) {
   }
 
   // SharedForm
-  CPDF_Metadata metaData;
-  metaData.LoadDoc(pDoc);
-  CXML_Element* pElement = metaData.GetRoot();
+  CPDF_Metadata metaData(pDoc);
+  const CXML_Element* pElement = metaData.GetRoot();
   if (pElement)
     CheckSharedForm(pElement, "workflowType");