lyrics: check if the song exists

src/helpers.h

@@ -52,7 +52,7 @@ inline MPD::Song *currentSong(BaseScreen *screen)
 {
 	MPD::Song *ptr = 0;
 	auto pl = proxySongList(screen);
-	if (pl)
+	if (pl && !pl.empty())
 		ptr = pl.currentSong();
 	return ptr;
 }

src/lyrics.cpp

@@ -107,6 +107,9 @@ void Lyrics::switchTo()
 #		endif // HAVE_CURL_CURL_H
 		
 		auto s = currentSong(myScreen);
+		if (!s)
+			return;
+
 		if (SetSong(*s))
 		{
 			SwitchTo::execute(this);