post sample rate changes directly on DSP input message queue. Removed sample source output queue entirely as it was not reliable under stress

plugins/samplesource/fcdproplus/fcdproplusinput.cpp

@@ -21,6 +21,7 @@
 #include <string.h>
 #include <errno.h>
 #include "dsp/dspcommands.h"
+#include "dsp/dspengine.h"
 #include "fcdproplusinput.h"
 
 #include "fcdproplusgui.h"
@@ -326,7 +327,7 @@ void FCDProPlusInput::applySettings(const Settings& settings, bool force)
 	if (signalChange)
     {
 		DSPSignalNotification *notif = new DSPSignalNotification(fcd_traits<ProPlus>::sampleRate, m_settings.centerFrequency);
-		getOutputMessageQueue()->push(notif);        
+		DSPEngine::instance()->getInputMessageQueue()->push(notif);
     }
 }