Fix wrong accumulator type - this fix makes the detector a little more sensitive, which is not necessarily good, but the previous accidental behaviour exaggerated the difference in results between float and double precision ffts

src/audiocurves/HighFrequencyAudioCurve.cpp

@@ -58,7 +58,7 @@ HighFrequencyAudioCurve::processFloat(const float *R__ mag, int)
 double
 HighFrequencyAudioCurve::processDouble(const double *R__ mag, int)
 {
-    float result = 0.0;
+    double result = 0.0;
 
     const int sz = m_lastPerceivedBin;