Don't run volume changing actions if there is no mixer

CHANGELOG.md

@@ -26,6 +26,7 @@
   synchronization attempts.
 * Support gstreamer's udpsink as a data source for visualization (Mopidy).
 * Deprecate `visualizer_fifo_path` in favor of `visualizer_data_source`.
+* Don't run volume changing actions if there is no mixer.
 
 # ncmpcpp-0.8.2 (2018-04-11)
 * Help screen: fixed display of EoF keycode

src/actions.cpp

@@ -621,11 +621,21 @@ void SlaveScreen::run()
 	drawHeader();
 }
 
+bool VolumeUp::canBeRun()
+{
+	return Status::State::volume() >= 0;
+}
+
 void VolumeUp::run()
 {
 	Mpd.ChangeVolume(static_cast<int>(Config.volume_change_step));
 }
 
+bool VolumeDown::canBeRun()
+{
+	return Status::State::volume() >= 0;
+}
+
 void VolumeDown::run()
 {
 	Mpd.ChangeVolume(-static_cast<int>(Config.volume_change_step));
@@ -1356,6 +1366,11 @@ void SetCrossfade::run()
 	Mpd.SetCrossfade(crossfade);
 }
 
+bool SetVolume::canBeRun()
+{
+	return Status::State::volume() >= 0;
+}
+
 void SetVolume::run()
 {
 	using Global::wFooter;

src/actions.h

@@ -428,6 +428,7 @@ struct VolumeUp: BaseAction
 	VolumeUp(): BaseAction(Type::VolumeUp, "volume_up") { }
 	
 private:
+	virtual bool canBeRun() override;
 	virtual void run() override;
 };
 
@@ -436,6 +437,7 @@ struct VolumeDown: BaseAction
 	VolumeDown(): BaseAction(Type::VolumeDown, "volume_down") { }
 	
 private:
+	virtual bool canBeRun() override;
 	virtual void run() override;
 };
 
@@ -791,6 +793,7 @@ struct SetVolume: BaseAction
 	SetVolume(): BaseAction(Type::SetVolume, "set_volume") { }
 	
 private:
+	virtual bool canBeRun() override;
 	virtual void run() override;
 };