little fix

[publicocean0]

sometimes seekpoint is undefined ... no seekpoints in memory

Decoder.prototype.seek = function(timestamp) {
var seekPoint;
seekPoint = this.demuxer.seek(timestamp);
if (seekPoint){
this.stream.seek(seekPoint.offset);
return seekPoint.timestamp;
} else return 0;
};

[master255]

yes! You right again! It fixs some problems