[core] proper check whether class is a TRef or TRefArray

Fixes https://its.cern.ch/jira/projects/ROOT/issues/ROOT-7052

Author: ferdymercury

core/meta/src/TStreamerElement.cxx

@@ -30,6 +30,7 @@
 #include "ThreadLocalStorage.h"
 #include "TList.h"
 #include "TRef.h"
+#include "TRefArray.h"
 #include "TInterpreter.h"
 #include "TError.h"
 #include "TObjArray.h"
@@ -305,8 +306,8 @@ TClass *TStreamerElement::GetClassPointer() const
 
 Int_t TStreamerElement::GetExecID() const
 {
-   //check if element is a TRef or TRefArray
-   if (strncmp(fTypeName.Data(),"TRef",4) != 0) return 0;
+   TClass* const type = GetClassPointer();
+   if (!type || !(type->InheritsFrom(TRef::Class()) || type->InheritsFrom(TRefArray::Class()))) return 0;
 
    //if the UniqueID of this element has already been set, we assume
    //that it contains the exec id of a TRef object.