Fix click/Pop sound on startup

Closes #908
  
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As suggested by @soyersoyer in https://github.com/probonopd/MiniDexed/issues/908#issuecomment-2848657586

Thanks @soyersoyer

src/minidexed.cpp

@@ -1414,6 +1414,8 @@ void CMiniDexed::ProcessSound (void)
 				// END create SampleBuffer for holding audio data
 
 				// get the mix of all TGs
+				arm_fill_f32(0.0f, SampleBuffer[indexL], nFrames);
+				arm_fill_f32(0.0f, SampleBuffer[indexR], nFrames);
 				tg_mixer->getMix(SampleBuffer[indexL], SampleBuffer[indexR]);
 
 				// BEGIN adding reverb