db/ProxyDatabasePlugin: read millisecond values for range start and end

Range `start` and `end` values in `mpd_song` (libmpdclient) is stored in
seconds only, which makes range times in `ProxySong` truncated to
seconds and leads to precision loss on satellite cue track range times.

This commit reads the added `start_ms` and `end_ms` value from
libmpdclient, which represent range start and end time in milliseconds.
And uses them to set `start_time` and `end_time` of `ProxySong`.

src/db/plugins/ProxyDatabasePlugin.cxx

@@ -211,8 +211,8 @@ ProxySong::ProxySong(const mpd_song *song)
 	if (_mtime > 0)
 		mtime = std::chrono::system_clock::from_time_t(_mtime);
 
-	start_time = SongTime::FromS(mpd_song_get_start(song));
-	end_time = SongTime::FromS(mpd_song_get_end(song));
+	start_time = SongTime::FromMS(mpd_song_get_start_ms(song));
+	end_time = SongTime::FromMS(mpd_song_get_end_ms(song));
 
 	const auto *af = mpd_song_get_audio_format(song);
 	if (af != nullptr) {