Threaded baseband source/sink stop before delete

sdrbase/dsp/threadedbasebandsamplesink.cpp

@@ -88,6 +88,7 @@ ThreadedBasebandSampleSink::ThreadedBasebandSampleSink(BasebandSampleSink* sampl
 
 ThreadedBasebandSampleSink::~ThreadedBasebandSampleSink()
 {
+    stop();
 	delete m_threadedBasebandSampleSinkFifo; // Valgrind memcheck
 	delete m_thread;
 }