valgrind: init m_scrollArea in vestige instrument

Closes #2041

plugins/vestige/vestige.cpp

@@ -78,6 +78,7 @@ vestigeInstrument::vestigeInstrument( InstrumentTrack * _instrument_track ) :
 	m_plugin( NULL ),
 	m_pluginMutex(),
 	m_subWindow( NULL ),
+	m_scrollArea( NULL ),
 	vstKnobs( NULL ),
 	knobFModel( NULL ),
 	p_subWindow( NULL )