Add default values for wxRichMessageDialog ctor arguments.

Both "caption" and "style" arguments were documented as having default values,
but didn't really have them. Fix this by actually adding them.

Closes #16524.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@77535 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/richmsgdlg.h

@@ -73,8 +73,8 @@ private:
     public:
         wxRichMessageDialog( wxWindow *parent,
                              const wxString& message,
-                             const wxString& caption,
-                             long style )
+                             const wxString& caption = wxMessageBoxCaptionStr,
+                             long style = wxOK | wxCENTRE )
             : wxGenericRichMessageDialog( parent, message, caption, style )
             { }