Fix NaNs in basic filters and Equalizer (#7141)

Fix several NaNs in the context of the basic filters and the Equalizer.

The coefficients of the `BiQuad` were not initialized which seems to have led to NaNs down the line.

Fix a division by zero in `EqEffect::peakBand` and `EqSpectrumView::paintEvent` if the energy is zero.

The condition `m_peakSum <= 0` was removed from `EqSpectrumView::paintEvent` because the value is initialized to 0 down the line and later only potentially positive values are added.

include/BasicFilters.h

@@ -144,7 +144,12 @@ template<ch_cnt_t CHANNELS>
 class BiQuad
 {
 public:
-	BiQuad() 
+	BiQuad() :
+		m_a1(0.),
+		m_a2(0.),
+		m_b0(0.),
+		m_b1(0.),
+		m_b2(0.)
 	{
 		clearHistory();
 	}