encoder/vorbis: generate end-of-stream packet before tag

Don't reset the ogg_stream_state object, because this discards the
end-of-stream packet that was just added.

src/encoder/vorbis_encoder.c

@@ -285,8 +285,6 @@ vorbis_encoder_pre_tag(struct encoder *_encoder, G_GNUC_UNUSED GError **error)
 	vorbis_analysis_init(&encoder->vd, &encoder->vi);
 	vorbis_block_init(&encoder->vd, &encoder->vb);
 
-	ogg_stream_reset(&encoder->os);
-
 	encoder->flush = true;
 	return true;
 }