Return nil instead of #wesnoth.playlist+1 when the current track is n…

…ot on the playlist

src/scripting/lua_audio.cpp

@@ -63,7 +63,15 @@ static int impl_music_get(lua_State* L) {
 		push_track(L, sound::get_current_track());
 		return 1;
 	}
-	return_int_attrib("current_i", sound::get_current_track() + 1);
+	if(strcmp(m, "current_i") == 0) {
+		size_t i = sound::get_current_track();
+		if(i == sound::get_num_tracks()) {
+			lua_pushnil(L);
+		} else {
+			lua_pushinteger(L, i + 1);
+		}
+		return 1;
+	}
 	// This calculation reverses the one used in [volume] to get back the relative volume level.
 	// (Which is the same calculation that's duplicated in impl_music_set.)
 	return_float_attrib("volume", sound::get_music_volume() * 100.0f / preferences::music_volume());