fix unused parameter warning introduced by last commit

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@45350 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/vscroll.h

@@ -621,7 +621,7 @@ protected:
     // unless the code has been updated to override OnGetRowHeight() instead,
     // this function must be overridden in the derived class and it should
     // return the height of the given row in pixels
-    virtual wxCoord OnGetLineHeight(size_t n) const
+    virtual wxCoord OnGetLineHeight(size_t WXUNUSED(n)) const
     {
         wxFAIL_MSG( _T("must be overridden if OnGetRowHeight() isn't!") );