player/Listener: add virtual method OnPlayerError()

Replaces two global idle_add() calls.

src/Partition.cxx

@@ -183,6 +183,12 @@ Partition::OnQueueSongStarted() noexcept
 	EmitIdle(IDLE_PLAYER);
 }
 
+void
+Partition::OnPlayerError() noexcept
+{
+	EmitIdle(IDLE_PLAYER);
+}
+
 void
 Partition::OnPlayerSync() noexcept
 {

src/Partition.hxx

@@ -277,6 +277,7 @@ private:
 	void OnQueueSongStarted() noexcept override;
 
 	/* virtual methods from class PlayerListener */
+	void OnPlayerError() noexcept override;
 	void OnPlayerSync() noexcept override;
 	void OnPlayerTagModified() noexcept override;
 	void OnBorderPause() noexcept override;

src/player/Control.cxx

@@ -19,6 +19,7 @@
 
 #include "Control.hxx"
 #include "Outputs.hxx"
+#include "Listener.hxx"
 #include "Idle.hxx"
 #include "song/DetachedSong.hxx"
 
@@ -190,6 +191,9 @@ PlayerControl::SetError(PlayerError type, std::exception_ptr &&_error) noexcept
 
 	error_type = type;
 	error = std::move(_error);
+
+	// TODO: is it ok to call this while holding mutex lock?
+	listener.OnPlayerError();
 }
 
 void

src/player/Listener.hxx

@@ -22,6 +22,12 @@
 
 class PlayerListener {
 public:
+	/**
+	 * A playback error has occurred and
+	 * PlayerControl::CheckRethrowError() will provide details.
+	 */
+	virtual void OnPlayerError() noexcept = 0;
+
 	/**
 	 * Must call playlist_sync().
 	 */

src/player/Thread.cxx

@@ -575,8 +575,6 @@ Player::OpenOutput() noexcept
 
 		pc.SetOutputError(std::current_exception());
 
-		idle_add(IDLE_PLAYER);
-
 		return false;
 	}
 
@@ -1065,8 +1063,6 @@ Player::PlayNextChunk() noexcept
 
 		pc.LockSetOutputError(std::current_exception());
 
-		idle_add(IDLE_PLAYER);
-
 		return false;
 	}