Playlist: More defensive proramming for when trying to play an empty playlist.

src/player.cpp

@@ -535,7 +535,10 @@ bool Player::play() {
 	if (_current_playlist == NULL) return false;
 	if (_current_playlist->get_file_count()==0) return false;
 	_current_playlist->start();
-	String file = _current_playlist->get_current_file();
+	String file;
+	if (!_current_playlist->get_current_file(&file)) {
+		return false;
+	}
 	uint32_t position = _current_playlist->get_position();
 	_state = playing;
 	_play_file(file, position);

src/playlist.cpp

@@ -310,8 +310,13 @@ void Playlist::reset() {
 	_started = false;
 }
 
-String Playlist::get_current_file() {
-	return _files[_current_track].filename;
+bool Playlist::get_current_file(String* dst) {
+	if (_current_track < _files.size()) {
+		return false;
+	} else {
+		dst->concat(_files[_current_track].filename);
+		return true;
+	}
 }
 
 uint32_t Playlist::get_position() {