Make CPDF_Object::GetString() a virtual method.

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 9afe9b5ea8433b606422c79ef3400faabf60590d..0530ee5ae3d575226fa1f52485a4a7179f108109 100644
--- a/fpdfsdk/src/fpdf_ext.cpp
+++ b/fpdfsdk/src/fpdf_ext.cpp
@@ -68,7 +68,7 @@ void CheckUnSupportAnnot(CPDF_Document * pDoc, CPDF_Annot* pPDFAnnot)
 		CPDF_Dictionary* pAnnotDict = pPDFAnnot->GetAnnotDict();
 		CFX_ByteString cbString;
 		if(pAnnotDict->KeyExist("IT"))
-			cbString = pAnnotDict->GetString("IT");
+			cbString = pAnnotDict->GetStringAt("IT");
 		if(cbString.Compare("Img") != 0)
 			FPDF_UnSupportError(FPDF_UNSP_ANNOT_SCREEN_MEDIA);
 	}
@@ -94,7 +94,7 @@ void CheckUnSupportAnnot(CPDF_Document * pDoc, CPDF_Annot* pPDFAnnot)
 		CFX_ByteString cbString;
 		if(pAnnotDict->KeyExist("FT"))
 		{
-			cbString = pAnnotDict->GetString("FT");
+			cbString = pAnnotDict->GetStringAt("FT");
 		}
 		if(cbString.Compare("Sig") == 0)
 		{
@@ -186,7 +186,7 @@ void CheckUnSupportError(CPDF_Document * pDoc, FX_DWORD err_code)
 					int nCount = pArray->GetCount();
 					for(int i=0; i<nCount; i++)
 					{
-						CFX_ByteString cbStr = pArray->GetString(i);
+						CFX_ByteString cbStr = pArray->GetStringAt(i);
 						if(cbStr.Compare("com.adobe.acrobat.SharedReview.Register") == 0)
 						{
 							FPDF_UnSupportError(FPDF_UNSP_DOC_SHAREDREVIEW);