GLSpectrum: set default waterfall share to 0.5

sdrbase/dsp/spectrumsettings.cpp

@@ -45,7 +45,7 @@ void SpectrumSettings::resetToDefaults()
 	m_histogramStroke = 30;
 	m_displayGridIntensity = 5;
 	m_displayTraceIntensity = 50;
-	m_waterfallShare = 0.66;
+	m_waterfallShare = 0.5;
 	m_displayCurrent = true;
 	m_displayWaterfall = true;
 	m_invertedWaterfall = true;