encoder: take control of the ogg_packet output from the Vorbis encoder

I'm not totally positive that this is necessary at this point, but it seems
safer that assuming it's not needed.

lib/encoder.js

@@ -269,6 +269,8 @@ Encoder.prototype._flushpacket = function (output, fn) {
   binding.vorbis_bitrate_flushpacket(this.vd, packet, function (rtn) {
     debug('vorbis_bitrate_flushpacket() return = %d', rtn);
     if (1 === rtn) {
+      packet.replace();
+
       // got a packet, output it
       // the consumer should call `pageout()` after this packet
       packet.pageout = true;