mixer/Listener: add `noexcept`

src/Partition.cxx

@@ -151,7 +151,7 @@ Partition::OnBorderPause() noexcept
 }
 
 void
-Partition::OnMixerVolumeChanged(gcc_unused Mixer &mixer, gcc_unused int volume)
+Partition::OnMixerVolumeChanged(Mixer &, int) noexcept
 {
 	InvalidateHardwareVolume();
 

src/Partition.hxx

@@ -257,7 +257,7 @@ private:
 	void OnBorderPause() noexcept override;
 
 	/* virtual methods from class MixerListener */
-	void OnMixerVolumeChanged(Mixer &mixer, int volume) override;
+	void OnMixerVolumeChanged(Mixer &mixer, int volume) noexcept override;
 
 	/* callback for #global_events */
 	void OnGlobalEvent(unsigned mask);

src/mixer/Listener.hxx

 /*
- * Copyright 2003-2018 The Music Player Daemon Project
+ * Copyright 2003-2019 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify
@@ -28,7 +28,8 @@ class Mixer;
  */
 class MixerListener {
 public:
-	virtual void OnMixerVolumeChanged(Mixer &mixer, int volume) = 0;
+	virtual void OnMixerVolumeChanged(Mixer &mixer,
+					  int volume) noexcept = 0;
 };
 
 #endif

test/NullMixerListener.hxx

 /*
- * Copyright 2003-2018 The Music Player Daemon Project
+ * Copyright 2003-2019 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * This program is free software; you can redistribute it and/or modify
@@ -24,7 +24,7 @@
 
 class NullMixerListener : public MixerListener {
 public:
-	void OnMixerVolumeChanged(Mixer &, int) override {}
+	void OnMixerVolumeChanged(Mixer &, int) noexcept override {}
 };
 
 #endif