base class must have virtual dtors and wxMBConv is no exception

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_4_BRANCH@17309 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/strconv.h

@@ -54,6 +54,9 @@ public:
     const wxCharBuffer cWC2WX(const wchar_t *psz) const { return cWC2MB(psz); }
     const wxWCharBuffer cWX2WC(const char *psz) const { return cMB2WC(psz); }
 #endif // Unicode/ANSI
+
+    // virtual dtor for any base class
+    virtual ~wxMBConv();
 };
 
 WXDLLEXPORT_DATA(extern wxMBConv) wxConvLibc;
@@ -115,7 +118,7 @@ public:
     virtual ~wxCSConv();
 
     wxCSConv& operator=(const wxCSConv& conv);
-    
+
     void LoadNow();
 
     virtual size_t MB2WC(wchar_t *buf, const char *psz, size_t n) const;