Performance improvement to the FFT + code cleanup + Added an option to select the FFT window

radio/src/fm_demod.h

@@ -154,14 +154,15 @@ public:
         }
     } 
 
-private:
     void setBandwidth(float bandWidth, bool updateWaterfall = true) {
+        bandWidth = std::clamp<float>(bandWidth, bwMin, bwMax);
         bw = bandWidth;
         _vfo->setBandwidth(bw, updateWaterfall);
         demod.setDeviation(bw / 2.0f);
         setAudioSampleRate(audioSampRate);
     }
 
+private:
     void setSnapInterval(float snapInt) {
         snapInterval = snapInt;
         _vfo->setSnapInterval(snapInterval);