Add a trivial virtual dtor to suppress g++ warnings.

Add a useless but virtual dtor to ValidationTraverserBase private class to
avoid g++ warnings.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73886 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/wincmn.cpp

@@ -2035,6 +2035,11 @@ public:
         return true;
     }
 
+    // Give it a virtual dtor just to suppress gcc warnings about a class with
+    // virtual methods but non-virtual dtor -- even if this is completely safe
+    // here as we never use the objects of this class polymorphically.
+    virtual ~ValidationTraverserBase() { }
+
 protected:
     // Called for each child, validator is guaranteed to be non-NULL.
     virtual bool OnDo(wxValidator* validator) = 0;