added wxMBConv::Clone() to be able to copy conversion objects polymorphically

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@38576 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/txtstrm.h

@@ -81,7 +81,7 @@ protected:
     char m_lastBytes[10]; // stores the bytes that were read for the last character
 
 #if wxUSE_UNICODE
-    wxMBConv m_conv;
+    wxMBConv *m_conv;
 #endif
 
     bool   EatEOL(const wxChar &c);
@@ -144,7 +144,7 @@ protected:
     wxEOL           m_mode;
 
 #if wxUSE_UNICODE
-    wxMBConv m_conv;
+    wxMBConv *m_conv;
 #endif
 
     DECLARE_NO_COPY_CLASS(wxTextOutputStream)