decoder/opus: limit the number of packets in _scan_stream()

src/decoder/plugins/OpusDecoderPlugin.cxx

@@ -444,10 +444,12 @@ mpd_opus_scan_stream(InputStream &is,
 	/* read at most 64 more pages */
 	unsigned remaining_pages = 64;
 
+	unsigned remaining_packets = 4;
+
 	bool result = false;
 
 	ogg_packet packet;
-	while (true) {
+	while (remaining_packets > 0) {
 		int r = ogg_stream_packetout(&os, &packet);
 		if (r < 0) {
 			result = false;
@@ -466,6 +468,8 @@ mpd_opus_scan_stream(InputStream &is,
 			continue;
 		}
 
+		--remaining_packets;
+
 		if (packet.b_o_s) {
 			if (!IsOpusHead(packet))
 				break;