Fix harmless gcc -Wextra warning in wxStringTokenizer.

Explicitly use the base class ctor.

src/common/tokenzr.cpp

@@ -85,6 +85,7 @@ wxStringTokenizer::wxStringTokenizer(const wxString& str,
 }
 
 wxStringTokenizer::wxStringTokenizer(const wxStringTokenizer& src)
+                 : wxObject()
 {
     DoCopyFrom(src);
 }