Fix release build crash in Reaper and Ableton Live

Source/PluginProcessor.cpp

@@ -178,6 +178,8 @@ PaulstretchpluginAudioProcessor::PaulstretchpluginAudioProcessor()
 PaulstretchpluginAudioProcessor::~PaulstretchpluginAudioProcessor()
 {
 	g_activeprocessors.erase(this);
+	m_thumb->removeAllChangeListeners();
+	m_thumb = nullptr;
 	m_bufferingthread.stopThread(1000);
 }