silence warning

git-svn-id: https://dng.biozentrum.unibas.ch/svn/openstructure/trunk@2606 5a81b35b-ba03-0410-adc8-b2c5c5119f08

modules/base/src/log_sink.hh

@@ -44,6 +44,7 @@ namespace {
 class DLLEXPORT_OST_BASE LogSink {
 public:
   LogSink(){};
+  virtual ~LogSink() { }
   virtual void LogMessage(const String& message, int severity = 0)=0;
 };