-Werror,-Wnon-virtual-dtor

This looks like a real bug, causing leaks in the derived VistaFilePickerImpl
(but harmless for the derived AsyncPickerEvents).

Change-Id: Ic0de3f56574b89fb45eccb09fb27b78427f712d4

fpicker/source/win32/filepicker/asyncrequests.hxx

@@ -120,6 +120,7 @@ typedef std::queue< RequestRef >  RequestQueue;
 class RequestHandler
 {
     public:
+        virtual ~RequestHandler() {}
         virtual void before() = 0;
         virtual void doRequest(const RequestRef& rRequest) = 0;
         virtual void after() = 0;