ServiceDVB - fix for subtitle track.

- do not try get subtitle track, when ddvd_get_spu_byid returns -1

lib/service/servicedvd.cpp

@@ -822,16 +822,25 @@ RESULT eServiceDVD::getSubtitleList(std::vector<struct SubtitleTrack> &subtitlel
 	{
 		struct SubtitleTrack track = {};
 		uint16_t spu_lang;
+
 		ddvd_get_spu_byid(m_ddvdconfig, spu_id, &spu_lang);
-		char spu_string[3]={(char) ((spu_lang >> 8) & 0xff), (char)(spu_lang & 0xff), 0};
-		eDebug("[eServiceDVD] getSubtitleList: spu_id=%d lang=%s", spu_id, spu_string);
-
-		track.type = 2;
-		track.pid = spu_id + 1;
-		track.page_number = 5;
-		track.magazine_number = 0;
-		track.language_code = spu_string;
-		subtitlelist.push_back(track);
+		if (spu_lang != 0xFFFF)
+		{
+			char spu_string[3] = {(char)((spu_lang >> 8) & 0xff), (char)(spu_lang & 0xff), 0};
+			eDebug("[eServiceDVD] getSubtitleList: spu_id=%d lang=%s", spu_id, spu_string);
+
+			track.type = 2;
+			track.pid = spu_id + 1;
+			track.page_number = 5;
+			track.magazine_number = 0;
+			track.language_code = spu_string;
+			subtitlelist.push_back(track);
+
+		}
+		else
+		{
+			eDebug("[eServiceDVD] getSubtitleList: spu_id=%d: invalid subtitle track", spu_id);
+		}
 	}
 	return 0;
 }