Fix compilation of <wx/archive.h> on Clang 19 on Fedora

Clang 19.1.0 on Fedora Rawhide fails to compile <wx/archive.h>
because m_rep's members are accessed as if m_rep was not a pointer,
but it is.

This is obviously wrong with any compiler, but apparently because
wxArchiveIterator is a template class, and its operator=() is
never called in tests, its brokenness went unnoticed.

include/wx/archive.h

@@ -217,9 +217,9 @@ public:
 
     wxArchiveIterator& operator =(const wxArchiveIterator& it) {
         if (it.m_rep)
-            it.m_rep.AddRef();
+            it.m_rep->AddRef();
         if (m_rep)
-            this->m_rep.UnRef();
+            m_rep->UnRef();
         m_rep = it.m_rep;
         return *this;
     }