ebml: fix GetDataStart() for elements with infinite size

--- ebml/ebml/EbmlMaster.h	2017-08-19 09:04:53.000000000 +0200
+++ ebml/ebml/EbmlMaster.h.datastart	2018-02-15 14:44:20.473862200 +0100
@@ -84,7 +84,7 @@ class EBML_DLL_API EbmlMaster : public E
     }
 
     uint64 GetDataStart() const {
-      return GetElementPosition() + EBML_ID_LENGTH((const EbmlId&)*this) + CodedSizeLength(GetSize(), GetSizeLength(), IsFiniteSize());
+      return GetElementPosition() + EBML_ID_LENGTH((const EbmlId&)*this) + CodedSizeLength(EbmlElement::GetSize(), GetSizeLength(), IsFiniteSize());
     }
 
     /*!